Introduction
Neoplasia of the canine nasal planum is rare. Effective treatment plans are predicated on obtaining an early diagnosis and pursuing therapy promptly. Squamous cell carcinoma (SCC) is the most common tumor diagnosed on the canine nasal planum.1 Due to the location and locally invasive behavior of these tumors, primary disease control is challenging and has been associated with a high rate of treatment-related complications.
Reported treatment options for local control of nasal planum SCC include surgical excision, radiation therapy (RT), cryoablation, intralesional injections, and electrochemotherapy.1–14 Surgical excision is considered the first-line therapy, despite the potential for drastic alterations in the dog’s appearance, as it provides the greatest opportunity for tumor control. Surgical treatment may be combined with systemic therapy such as chemotherapy and NSAIDs, depending on tumor characteristics and the identification of factors associated with increased metastatic potential.
The literature describing clinical characteristics and outcomes associated with the treatment of dogs with nasal planum SCC is lacking. Additionally, while the prognosis following surgical treatment in dogs with nasal planum SCC is generally considered good, there is little evidence to support this assertion. The primary objective of this study was to describe the clinical characteristics, specific treatment types and associated complications, and overall outcomes in a relatively large cohort of dogs diagnosed with nasal planum SCC that underwent local treatment.
Methods
Animals
A retrospective, multi-institutional study was performed. The medical record databases of 13 referral veterinary clinics were searched to identify dogs diagnosed with nasal planum SCC. Dogs were included if a histopathological diagnosis of SCC of the nasal planum was obtained and a definitive type of local therapy was performed at the referral institution. Dogs that had undergone local treatment prior to referral were excluded. Additionally, dogs with SCC of the oral cavity, nasal cavity, or skin of the face were excluded.
Medical records review
Variables recorded from the medical records included signalment, type and duration of clinical signs, comorbidities, physical examination findings, tumor characteristics, clinical pathology results, diagnostic imaging results, local (surgery, RT, intralesional therapy, electrochemotherapy) and systemic (NSAIDs, chemotherapy) treatment modalities, results and adverse events, histopathology results, disease progression (ie, tumor recurrence and/or metastasis), and outcome. Complete staging was defined as the following: clinical laboratory testing, thoracic and skull imaging (CT and/or radiographs), and regional lymph node sampling performed within 4 weeks prior to local treatment. Response to RT was defined by the Response Evaluation Criteria in Solid Tumors, with categories including complete response, partial response, stable disease, and progressive disease. All treatment-related complications were categorized and graded with the Veterinary Cooperative Oncology Group and Veterinary Radiation Therapy Oncology Group criteria and grading schemes.15,16
Metastatic progression was classified according to specific definitions assigned for the terms new metastasis and progressive metastasis. New metastasis was defined as imaging, cytologic, or histopathologic findings consistent with new metastatic disease in a dog with no evidence of metastatic disease at that location at the time local therapy was instituted. Progressive metastasis was defined as imaging, cytologic, or histopathologic findings consistent with progressive metastatic disease in a dog previously diagnosed with metastatic disease at that location at the time of instituting local therapy. This included worsening metastatic disease at a previously diagnosed site.
Local recurrence was defined as cases that had complete resolution of gross disease after completing any form of local therapy followed by tumor recurrence visualized at a recheck examination. Disease progression was defined as new or progressive growth/metastasis or local recurrence, and progression-free interval was defined as the time from the initiation of local treatment to the first documentation of new metastasis, local recurrence, progressive growth in a dog without a complete response to local treatment, progressive metastasis, or death attributed to tumor.
Statistical analysis
Summary statistics were generated for all measured variables. Categorical variables were expressed as numbers and percentages. Normal distribution of continuous variables was assessed with histograms and tests of skewness and kurtosis, and variable data were expressed as means and SDs or medians and ranges or IQRs. The Fisher exact test was used to compare the distribution of dogs that experienced RT side effects according to type of radiation treatment received (palliative, definitive, stereotactic).
Progression-free intervals were estimated with the Kaplan-Meier product-limit method. Dogs that did not experience the previously described events during the follow-up period were censored at their last known alive dates (if alive or lost to follow-up) or at their date of death (if death was not attributed to tumor). Cox proportional hazards regression was used to estimate risk factors for disease progression as defined previously. The following risk factors for progression were analyzed: local treatment type, use of chemotherapy, use of an NSAID, tumor size, tumor ulceration, tumor crossing midline, tumor extending internally, metastasis at diagnosis, and incomplete histologic margin. Univariable analyses were performed, and variables with P < .20 were tested for inclusion into a best-fit multivariable model.
Overall survival time was defined as the interval from the onset of local treatment until death from any cause and was estimated with the Kaplan-Meier product-limit method, with dogs alive or lost to follow-up censored at their last known alive dates. The log-rank test was used to compare unadjusted survival time according to whether disease progression was documented following local therapy. Cox proportional hazards regression was used to estimate risk factors for overall survival as defined previously. The following risk factors for overall survival were analyzed: local treatment type, use of chemotherapy, use of an NSAID, tumor size, tumor ulceration, tumor crossing midline, tumor extending internally within the nasal cavity, metastasis at diagnosis, and incomplete histologic margin. Univariable analyses were performed, and variables with P < .20 were tested for inclusion into a best-fit multivariable model. All tests were 2-sided, and P < .05 was considered statistically significant.
Results
Dogs
From the years 2003 to 2020, 89 dogs were identified that met the inclusion criteria. The veterinary clinics contributing cases included the College of Veterinary Medicine and Biomedical Sciences, Colorado State University; College of Veterinary Medicine, University of Missouri; College of Veterinary Medicine, University of Florida; College of Veterinary Medicine, The Ohio State University; School of Veterinary Medicine, University of California-Davis; Ontario Veterinary College, University of Guelph; College of Veterinary Medicine, Washington State University; College of Veterinary Medicine, University of Tennessee; School of Veterinary Medicine, Texas A&M University; Alta Vista Animal Hospital; College of Veterinary Medicine, University of Illinois Urbana-Champaign; and College of Veterinary Medicine, University of Georgia. The median age of dogs was 10.4 years (range, 4.7 to 14.7 years), and the median weight was 36.4 kg (range, 9.5 to 69.2 kg). There were 21 different breeds, with Labrador Retrievers and Golden Retrievers representing 33 of 89 (37%) and 21 of 89 dogs (24%), respectively. There were 16 intact male, 56 castrated male, 2 intact female, and 15 spayed female dogs.
History and clinical signs
The most common presenting complaints included a visible mass on the nasal planum (80 of 89 [89%]), sneezing (56 of 89 [62%]), ulceration of the nasal planum (49 of 89 [54%]), epistaxis (39 of 89 [43%]), nonhemorrhagic nasal discharge (31 of 89 [34%]), and visible muzzle deformity (25 of 89 [27.8%]). Less common clinical signs included dyspnea (9 of 89 [10%]), cough (6 of 89 [7%]), stertor (5 of 89 [6%]), nasal petechiae (3 of 89 [3%]), muzzle malodor (3 of 89 [3%]), head shaking (3 of 89 [3%]), self-trauma/excoriations (3 of 89 [3%]), ocular discharge (3 of 89 [3%]), decreased nasal air flow (2 of 89 [2%]), decreased appetite/weight loss (2 of 89 [2%]), hair loss (1 of 89 [1%]), polyuria/polydipsia (1 of 89 [1%]), and stridor (1 of 89 [1%]).
Physical examination
Tumor measurements based on the diameter of the visible mass obtained during physical examination were available for 37 dogs; the median size was 15 mm (range, 5 to 120 mm). Tumor ulceration was present in 49 of 89 dogs (54%). The majority of tumors extended internally (51 of 89 dogs [57%]), and 29 of 89 (33%) crossed midline. Enlarged local lymph nodes were palpated in 41 of 89 dogs (46%).
Diagnostic results
Relevant pretreatment diagnostic results were reviewed and categorized for staging purposes. Full staging was completed in 73 of 89 dogs (81%), with 72 of 73 (99%) and 25 of 73 dogs (34%) having thoracic radiographs and thoracic CT images obtained, respectively. Additionally, the following diagnostics were performed: radiographs of head (9 of 89 [10%]), CT of head (80 of 89 [90%]), MRI of head (5 of 89 [6%]), cervical ultrasound (5 of 89 [6%]), abdominal ultrasound (17 of 89 [19%]), aspiration of mandibular lymph nodes (76 of 89 [85%]), and aspiration of retropharyngeal lymph nodes (8 of 89 [9%]).
Of the dogs that were fully staged, regional and/or distant metastasis was detected in 9 of 73 staged dogs (12%). Metastasis was diagnosed via cytology or imaging in the following locations: thoracic CT in 4 of 9 (44%), cytology of regional lymph nodes in 2 of 9 (22%), thoracic radiographs in 1 of 9 (11%), abdominal ultrasound in 1 of 9 (11%), and cytology of regional lymph nodes and thoracic CT in 1 of 9 dogs (11%). Evaluation of preoperative blood work results did not provide additional, relevant conclusions related to clinical staging and were therefore omitted from further analysis.
Local treatments
Local therapy consisted of surgical excision alone in 63 of 89 dogs (71%), RT alone in 20 of 89 (22%), surgical excision in combination with neoadjuvant (2) and adjuvant (2) external-beam RT in 4 of 89 (4%), surgical excision and adjuvant superficial RT (plesiotherapy [strontium 90]) in 1 of 89 (1%), and intratumoral cisplatin chemotherapy in 1 of 89 (1%). The 5 cases that underwent surgery in combination with external-beam RT or plesiotherapy were included in the surgery cohort when divided by the form of local therapy.
In dogs undergoing surgery, operative intent was categorized as wide excision in 63 of 68 (93%) and marginal excision in 5 of 68 dogs (7%). In 37 of 68 dogs (54%), the incisive bone was excised with the tumor. Histopathologic margins were complete in 49 of 68 (72%) and incomplete in 19 of 68 dogs (28%). Intraoperative complications occurred in 22 of 68 dogs (32%) and were graded as shown in Table 1. These included hemorrhage (22 of 22 [100%]) and iatrogenic injury to the surface of the tongue with the oscillating saw during the maxillary osteotomy (1 of 22 [5%]).
Intraoperative complications in 68 dogs undergoing surgery, according to the Veterinary Cooperative Oncology Group—Common Terminology Criteria for Adverse Events.
| Complication | Grade 1 | Grade 2 | Grade 3 | Grade 4 | Grade 5 |
|---|---|---|---|---|---|
| Hemorrhage | 15 (22.1) | 6 (8.8) | 1 (1.5) | — | — |
| Iatrogenic injury | — | 1 (1.5) | — | — | — |
Data are presented as number (%) of complications.
Postoperative complications were documented in 45 of 68 dogs (66%), with hemorrhage (15 of 68 [22%]) and bilateral epistaxis (14 of 68 [21%]) being most common (Table 2). Additional postoperative complications included the following: unilateral epistaxis, dyspnea, anorexia, labial ulcer, seroma, dehiscence, surgical site infection, nasal stenosis, oronasal fistula, self-trauma, poor cosmesis, deviated orifice, altered prehension, nonhemorrhagic nasal discharge, and swelling. Most of the complications developed during the immediate postoperative hospitalization period; however, specific examples including dehiscence, infection, and oronasal fistula were recorded at long-term follow-up visits. Most complications (102 of 129 [79%]) following surgical treatment were considered minor (≤ grade 2).
Postoperative complications in 68 dogs undergoing surgery, according to the Veterinary Cooperative Oncology Group—Common Terminology Criteria for Adverse Events.
| Complication | Grade 1 | Grade 2 | Grade 3 | Grade 4 | Grade 5 |
|---|---|---|---|---|---|
| Hemorrhage | 15 (22.1) | 3 (4.4) | 2 (2.9) | — | — |
| Unilateral epistaxis | 1 (1.5) | 2 (2.9) | — | — | — |
| Bilateral epistaxis | 14 (20.6) | 2 (2.9) | 2 (2.9) | — | — |
| Dyspnea | 5 (7.4) | 1 (1.5) | — | — | — |
| Anorexia | 8 (11.8) | 1 (1.5) | 1 (1.5) | — | — |
| Labial ulcer | 4 (5.8) | 1 (1.5) | — | — | — |
| Seroma | 2 (2.9) | — | — | — | — |
| Dehiscence | 6 (8.8) | 6 (8.8) | 8 (11.8) | 1 (1.5) | — |
| Surgical site infection | 3 (4.4) | — | 5 (7.4) | — | — |
| Nasal stenosis | 4 (5.8) | 1 (1.5) | 3 (4.4) | — | — |
| Oronasal fistula | — | 2 (2.9) | — | — | — |
| Self-trauma | 3 (4.4) | 1 (1.5) | 1 (1.5) | — | — |
| Poor cosmesis | 1 (1.5) | — | — | 1 (1.5) | — |
| Deviated orifice | 2 (2.9) | — | — | — | — |
| Change in eating | 6 (8.8) | 2 (2.9) | 1 (1.5) | 1 (1.5) | — |
| Nonhemorrhagic nasal discharge | 2 (2.9) | 1 (1.5) | 1 (1.5) | — | — |
| Swelling | 3 (4.4) | — | — | — | — |
Data are presented as number (%) of complications.
Dogs undergoing RT were subdivided based on treatment protocol: palliative RT in 11 of 24 (46%), definitive fractionated RT in 9 of 24 (38%), and stereotactic RT in 4 of 24 dogs (17%). Nonetheless, individual dosing regimens still varied substantially within each subgroup. Among 11 dogs that underwent palliative RT, 7 had 4 fractions of 800 cGy, 1 had 2 fractions of 400 cGy, 1 had 4 fractions of 600 cGy, 1 had 5 fractions of 600 cGy, and 1 protocol was not recorded. Median total palliative RT dose was 3,200 cGy (range, 800 to 3,200 cGy). Among 9 dogs that underwent definitive fractionated RT, several different protocols were used ranging from 10 to 20 fractions, 285 to 400 cGy/dose, and a median total definitive RT dose of 5,400 cGy (range, 4,000 to 8,000 cGy). Among 4 dogs that underwent stereotactic RT, 1 dog had 1 fraction of 1,200 cGy and 3 dogs had 3 fractions of 1,000 cGy. Median total stereotactic dose was 3,000 cGy (range, 1,200 to 3,000 cGy).
Palliative RT treatment response was assessed as partial response in 7 dogs, stable disease in 3 dogs, and progressive disease in 1 dog. Definitive fractioned RT treatment response as the only form of local therapy was assessed as complete response in 1 dog, partial response in 2 dogs, and stable disease in 1 dog and was not reported in 5 dogs. Stereotactic RT response as the sole form of local therapy was assessed as complete response in 1 dog, partial response in 1 dog, and stable disease in 2 dogs. Only 2 dogs undergoing RT for gross disease (1 dog with definitive RT and 1 dog with stereotactic RT) experienced a complete response. Of the 2 dogs that had a complete response, the dog that underwent definitive RT developed local recurrence, whereas the dog that underwent stereotactic RT did not. The dog that underwent neoadjuvant stereotactic RT achieved a partial response, whereas the dog that received definitive RT demonstrated progressive disease.
Radiation therapy treatment–related complications were documented in 19 of 24 dogs (79%), with RT site infections being most common in 15 of 24 dogs (63%). Less common complications included mucous membrane pathology (5 of 24 [21%]), anorexia (2 of 24 [8%]), unacceptable cosmesis (1 of 24 [4%]), epistaxis (1 of 24 [4%]), surgical site dehiscence at biopsy site (1 of 24 [4%]), bone pathology (1 of 24 [4%]), keratoconjunctivitis sicca (1 of 24 [4%]), and nasal discharge (1 of 24 [4%]). There were no reports of oronasal fistula formation, treatment site stenosis, altered prehension, or death secondary to RT. The incidence of complications varied based on RT type, with 8 of 11 dogs (73%) treated with palliative RT, 9 of 9 dogs (100%) treated with definitive RT, and 2 of 4 dogs (50%) treated with stereotactic RT experiencing side effects.
Systemic treatments
Systemic chemotherapy was administered to 27 of 89 dogs (30%) following some form of local therapy. Case selection, including the specific indications for treatment (eg, disease stage at diagnosis), varied, as did the 23 of 27 protocols (85%) available for review. Chemotherapy drugs utilized included carboplatin (16 of 23 [70%]), toceranib (6 of 23 [26%]), cyclophosphamide (3 of 23 [13%]), fluorouracil (2 of 23 [9%]), rapamycin (2 of 23 [9%]), pamidronate (1 of 23 [4%]), and bleomycin (1 of 23 [4%]). One dog (1 of 89 [1%]) received a single dose of intratumoral cisplatin as part of a clinical trial, and 1 dog (1 of 89 [1%]) received 2 doses of bleomycin electrochemotherapy. Nonsteroidal anti-inflammatory drugs were administered to 51 of 89 dogs (57%).
Disease progression and outcomes
At the time of study completion, 43 dogs had died (median follow-up time, 248 days; range, 3 to 1,825 days; IQR, 153 to 458), 10 dogs were alive (median follow-up time, 379 days; range, 14 to 1,044 days; IQR, 379-623), and 37 dogs were lost to follow-up (median follow-up time, 90 days; range, 1 to 1,367 days; IQR, 30 to 293).
Local recurrence was reported in 19 of 89 dogs (21%), including 16 of 63 dogs (25%) treated with surgery alone. In one of the dogs with a complete response to RT alone, recurrence occurred approximately 1 year after completion of RT. Recurrence also occurred in 1 of 4 dogs (25%) treated with surgery and RT and 1 of 1 dog (100%) treated with surgery and plesiotherapy.
After local therapy, some level of continued staging (not complete in all dogs) was performed in all but 4 dogs. As cases from many clinics were included in this study, it was not possible to determine what recommendations for staging after local therapy were made for each case. Four dogs with metastasis diagnosed at the onset of local treatment developed progressive metastasis, documented at 44 days, 120 days, 205 days, and 260 days after treatment completion. Fifteen dogs developed new metastases following local therapy; 6 of those dogs had received chemotherapy. A time frame was reported in 10 of these dogs, with a median time to diagnosis of 297 days (range, 26 to 537 days; IQR, 56 to 405).
Overall, disease progression was documented in 33 of 89 dogs (37%), including 2 dogs with progressive metastasis and local recurrence, 5 dogs with new metastasis and local recurrence, 12 dogs with local recurrence with no new metastasis, 5 dogs with progressive growth from a tumor that did not undergo a complete response, 1 dog with progressive metastasis and no recurrence, 1 dog with new and progressive metastasis and no recurrence, and 7 dogs with new metastasis and no recurrence. Furthermore, 15 dogs died without documented disease progression despite the cause of death being attributed to the tumor in the medical record. The remaining 41 dogs had no documented disease progression during the follow-up period and were either alive or lost to follow-up or had died due to causes unrelated to the disease process.
The median progression-free interval was 237 days (95% CI, 198 to 405). Prognostic indicators, including the presence of metastasis at diagnosis (hazard ratio [HR], 3.00; 95% CI, 1.24 to 7.21; P = .014) and a tumor that crosses midline of the nasal planum (HR, 2.22; 95% CI, 1.22 to 4.04; P = .009), were associated with the hazard of progression on multivariable analysis.
The median survival time (MST) of all dogs was 452 days (95% CI, 285 to 576). The MST among 33 dogs with documented disease progression was 336 days (95% CI, 189 to 458) versus 685 days (95% CI, 334 to 1,042) among 56 dogs that did not have documented disease progression (Figure 1), which was significantly different (P = .0038). Documented disease progression was significantly associated with hazard of death (HR, 1.93; 95% CI, 1.03 to 3.63; P = .041), whereas no other prognostic factors for death were identified.
Kaplan-Meier survival curve for dogs with and without documented disease progression.
Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.10.0642
Discussion
This study provides the most comprehensive description to date of pretreatment staging results associated with nasal SCC and demonstrated that dogs undergoing surgical excision of nasal planum SCC could have a favorable outcome. The challenging surgical location of nasal planum SCC and concerns regarding unsatisfactory cosmesis are major factors influencing local disease management and outcome. Previous concerns regarding the postoperative physical appearance were not recognized in this study, as only 2 owners (out of 68 dogs undergoing surgery) felt that the physical appearance was unacceptable. Additionally, while complications were common, most were considered minor. Long-term follow-up demonstrated a relatively low recurrence rate (21%), which was not associated with whether a complete surgical margin was obtained. Local recurrence was associated with shorter MSTs, further demonstrating the importance of aggressive local therapy for long-term disease control. Lastly, due to a relatively high posttreatment metastatic rate noted in this study, adjunctive therapies warrant consideration for both local and systemic disease management.
The majority of dogs in this study presented for clinical signs related to local disease, with Labrador Retrievers and Golden Retrievers representing the most common breeds. These findings are similar to prior studies2,5,7,11 that report epistaxis and sneezing as the most common presenting complaint and show that nasal planum SCC is overrepresented in those breeds.
Once a diagnosis of SCC was confirmed, complete staging was performed as part of the preoperative diagnostics in approximately 80% of cases. Metastatic disease was found in only 12% of these cases, affirming the locally aggressive but slow-to-metastasize biological behavior of this tumor.7,11 These results supported an aggressive approach to local control, as the disease process is often confined to the nasal planum, suggesting local treatment may provide long-term benefit.
Surgical resection was performed in the majority of cases and associated with positive outcomes, despite difficulties in obtaining tumor-free margins. Curative intent surgeries were attempted in 93% of the cases; however, complete histopathologic margins were reported in 72% of the biopsy submissions. A previous study1 evaluating cosmetic nasal reconstruction outcomes following nasal planum resection reported 88% tumor-free margins; however, this was a different study population that included multiple tumor types and was limited to cases that could be appropriately treated with a conservative surgical approach. Many cases in the current study required more aggressive surgical resections, such as an incisivectomy, which was performed in 54% of dogs. Regardless of the approach, inherent challenges result from the complex local anatomy, invasive nature of the tumor, and concerns regarding cosmesis that must be considered during surgery. In cases of incomplete margins, surgical revision should be considered whenever possible. If no option exists, there may be a role for adjuvant RT. A prior study7 reports a poor outcome (MST of 14 weeks) with the use of postoperative RT; however, this is based on only 7 cases and older treatment protocols. In the current study, 3 dogs underwent RT following incomplete surgical margins and 1 dog developed local recurrence.
Minor surgical complications were common and more likely to occur postoperatively as opposed to intraoperatively. Hemorrhage was the most frequent intraoperative complication and a result of the highly vascular nature of the affected region. Only 1 dog experienced grade 3 hemorrhage and required a transfusion. In the remaining dogs, bleeding was considered minor and did not require any additional interventions. A prior study7 also reports intraoperative hemorrhage as a complication; however, most descriptions are limited. Intraoperative hemorrhage is unavoidable when performing surgery in this area, but meticulous hemostasis may help mitigate the severity and impact.
Postoperative complications were reported in 66% of cases with hemorrhage from the surgical site and bilateral epistaxis being the most common. Previous studies1,7,11 report a similarly high incidence of postoperative bleeding, which is likely a result of the frequent, unavoidable movement of the surgical site combined with dense tissue vascularity of the muzzle. Basic functions such as eating, drinking, and even the passage of air may disrupt the fragile blood vessels and cause minor hemorrhage. Nevertheless, owners should be informed of this common complication, as it may require additional days in the hospital and household adjustments prior to discharge. Most other postoperative complications were related to healing of the surgical site or alterations in prehension and were self-limiting. Dehiscence and surgical site infection were common and, historically, are often associated with maxillofacial surgeries.4,17 In a prior study,1 incisional dehiscence was the most common complication and reported in 50% of cases. The constant movement, exposure to foreign material (eg, food), and the potential for closures to be performed under tension are likely all contributing factors. Adherence to proper surgical techniques will help mitigate the likelihood of postoperative tissue tension, and specific steps such as use of local mucosal flaps, releasing incisions, or an ostectomy of sharp bone edges should be employed when necessary. Altered prehension should be expected as the dog adapts to changes in the anatomy of the muzzle and may be exacerbated by challenges with smelling food if inflammation and blood clots are obstructing the nasal passages. The majority of these complications (79%) were considered minor and did not require additional treatment. More severe (grade 3 or 4) complications were recorded in 27% of dogs postoperatively, with dehiscence and surgical site infection being most common. These dogs required intervention, including revision of the dehisced surgical site or antibiotic therapy, all of which resulted in complete resolution. Despite the relatively high incidence of surgical complications, most are self-limiting or easily treatable, which is an important point to communicate to owners.
Radiation therapy was highly individualized and included primary and (neo)adjuvant therapy, with definitive and palliative protocols, as well as plesiotherapy and stereotactic RT. Of the 20 dogs that underwent RT as the primary form of treatment, 2 (10%) experienced a complete response and 10 (50%) experienced a partial response. Overall, tumor size decreased in 12 dogs (60%) that underwent RT as the primary therapy, suggesting a moderate benefit exists in the majority of cases. By comparison, gross disease was removed in all surgical cases, which supported surgery as the most effective form of local therapy.
A complication rate of 79% was noted with RT cases. Complication types differed between surgery and RT, with treatment site infections being most common (63%) following radiation. This was likely a result from the local tumor necrosis caused by the treatment. Significant differences were present in the incidence of complications depending on the type of RT; definitive RT was associated with highest complication rate, followed by palliative RT, then stereotactic RT. These findings should be discussed with the owners when considering the treatment course best suited for their individual goals.
Various reconstructive techniques1–3,9,10 have been described in an attempt to improve postoperative cosmesis and owner satisfaction and have shown promising results. The specific reconstructive technique employed was not evaluated in this study; however, the rate of post–surgical-treatment unacceptable appearance was low (3%), suggesting prior conceptions related to poor postoperative cosmesis may be unfounded. Regardless of the therapy employed, client education regarding the nature of the physical appearance after treatment is imperative prior to initiating treatment.
Systemic therapies, including NSAIDs and chemotherapeutics, were employed in 57% and 30% of dogs, respectively. The presence of the cyclooxygenase-2 expression has been documented in SCC, suggesting NSAID therapy has a potential role. Additionally, the efficacy of chemotherapy was evaluated in a study18 of 8 dogs that received alternating doses of doxorubicin, carboplatin, and oral piroxicam; however, it should be noted that the dogs of that study did not have distinct nasal planum exclusive SCC and were diagnosed with intranasal/sinonasal tumors. The results were promising, as 4 dogs had a complete remission, 2 dogs had a partial remission, and 2 dogs had stable disease. Further studies are required to determine the proper case selection and treatment protocol. Alternative local therapies, such as intratumoral chemotherapy13 or electrochemotherapy,17 have been reported and were used in isolated cases in this study. The role of these and other innovative therapies is an area of active research and may provide options for owners that are unwilling to pursue traditional treatment strategies or may be used in conjunction with traditional modalities.
The 25% recurrence rate (with surgery alone) reiterated the local treatment challenges encountered with nasal planum SCC. As discussed, achieving complete surgical margins is difficult, particularly with larger, more invasive tumors, and was successful in approximately three-fourths of the cases in this study. Prior reports5,7,11 have demonstrated an association between incomplete surgical margins and local tumor recurrence; however, this relationship was not present in our study, as an incomplete resection was not shown to be a hazard of disease progression. A previous study7 has also suggested that tumor grade does not have prognostic value, but this has not been directly evaluated. Further histologic investigation should be considered to identify possible risk factors for local recurrence and overall outcome. In addition to tumor size, certain tumor locations have been associated with higher rates of recurrence, specifically those that extend ventral to the nasal vestibule.11 These tumors typically require an incisivectomy for curative intent surgery and may be associated with a higher incidence of complications, including unsatisfactory cosmesis for owners. The low rate of cosmetic concerns reported in this study and development of novel reconstructive techniques2,11,19–22 suggested that greater emphasis can be placed on attaining complete margins through larger resections. Advanced diagnostics, including a CT scan and, in select cases, rhinoscopy, could be considered to optimize the understanding of tumor anatomy prior to surgery.11 Local recurrence was negatively correlated with overall survival time in our study, further supporting the importance and challenges related to local disease control.
Local recurrence represented the most common form of disease progression; however, a small subset of dogs developed metastasis with or without tumor recurrence. Metastasis at the time of diagnosis and having a tumor that crossed midline were identified as 2 risk factors significantly associated with a shorter progression-free interval. This study systematically evaluated the presence and impact of metastasis in nasal planum SCCs, with the results suggesting that there may be a subset of tumors that is more prone to disease spread. Proper staging may aid in identifying these cases, which will improve the overall understanding of the case and potentially guide therapeutic decisions. Long-term data showed that approximately 20% of the dogs in this study developed new or progressive metastatic disease during the follow-up period. Previous studies5,10 have documented isolated cases of metastasis, and the overall rate was generally considered rare; however, a more recent study1 of 26 dogs reported a similar metastatic rate (23%) to the current study. Adjunctive therapies (chemotherapy) and regimented monitoring plans warrant consideration in light of these findings. At a minimum, clinicians should communicate the negative prognostic impact associated with identifying metastasis at diagnosis to owners. A similar discussion should occur with owners when the dog has a tumor that crosses midline. The median progression-free interval of 237 days identified in this study provides additional, previously unreported information to clinicians and owners alike.
The MST of dogs with disease progression was shown to be approximately half that of dogs without progression. This provides insight into the biological behavior of the disease by identifying local recurrence and/or metastasis as key negative prognostic indicators. This is likely a result of the limited and largely ineffective local and systemic treatment options available for these cases after initial local therapy. Specifically, surgical revision is rarely possible and the current understanding of effective adjunctive treatment options remains deficient.
Several limitations should be recognized in this study. Data were collected retrospectively, and there were inherent inaccuracies that could have occurred during the recording of this information. Additionally, while there were benefits to having numerous clinics contribute cases, there was also variability in how records were maintained and the logistics of care that was provided to dogs. Lastly, while the total number of dogs included in this study was relatively high, these were subdivided into different categories of local treatments, leading to smaller numbers of dogs for each comparison.
The results of this study demonstrated that dogs undergoing local treatment of nasal planum SCC have a favorable prognosis. Whenever possible, surgical resection should be considered, as it provides the greatest possibility for primary disease control. Alternative forms of local treatment, including RT, can be considered in nonsurgical cases or as an adjunct for incomplete resections. Despite a high rate of treatment-related complications, most were mild and self-limiting and should not preclude an aggressive surgical approach aimed at maximizing local tumor control. Additional adjunctive therapy targeting both regional and systemic disease should be considered in certain cases and warrants further investigation.
Acknowledgments
None reported.
Disclosures
Dr. Wustefeld-Janssens is a member of the JAVMA Scientific Review Board, but was not involved in the editorial evaluation of or decision to accept this article for publication.
No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
ORCID
W. T. N. Culp https://orcid.org/0000-0001-6132-156X
T. Martin https://orcid.org/0000-0002-9258-4861
K. G. Mathews https://orcid.org/0000-0003-3431-6049
O. Skinner https://orcid.org/0000-0002-3765-429X
L. E. Selmic https://orcid.org/0000-0001-6695-6273
J. Dornbusch https://orcid.org/0000-0001-5445-5973
H. Phillips https://orcid.org/0000-0002-3291-0266
M. Wallace https://orcid.org/0000-0002-5286-4287
M. A. Steffey https://orcid.org/0000-0003-0852-0644
M. S. Kent https://orcid.org/0000-0002-7703-7720
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