Objective—To develop a reverse transcriptase-polymerase
chain reaction (RT-PCR) assay to detect
canine melanoma-associated antigens (MAAs) and to
use this technique to screen aspirates of lymph
nodes (LNs) for evidence of metastatic spread of oral
Animals—7 dogs with oral malignant melanoma and
4 dogs with multicentric lymphosarcoma.
Procedures—We prepared cDNA from melanoma
tumor biopsies and fine-needle aspirates obtained
from submandibular LNs of dogs with oral malignant
melanoma or multicentric lymphosarcoma. The RTPCR
assay was performed by use of tyrosinase,
Melan-A, gp100, tyrosinase-related protein 2 (TRP-2),
or melanoma antigen-encoding gene B (MAGE-B)-
Results—We detected MAGE-B mRNA in canine testicular
tissue but not in melanoma biopsy specimens.
Tyrosinase, Melan-A, gp100, and TRP-2 mRNAs were
detected in tumor biopsy specimens and in 2 of 5 LN
aspirates from dogs with melanoma, suggesting
metastatic spread in those 2 dogs. We did not detect
MAAs in LN aspirates obtained from dogs with multicentric
lymphosarcoma. Sequencing of canine Melan-
A and gp100 PCR products confirmed the specificity
of the assay for these genes.
Conclusions and Clinical Relevance—Clinical staging
of dogs with oral malignant melanoma is useful to
assist in designing appropriate treatments. However,
results of histologic examination of LN biopsy specimens
can be inconclusive and, in humans, can underestimate
the number of patients with metastatic disease.
Molecular staging of melanomas in dogs can be
achieved by screening LN aspirates for MAA mRNA,
and this can be performed in combination with cytologic
examination to aid in detection of metastatic disease.
( Am J Vet Res 2003;64:544–549)
Objective—To characterize variability in melanoma-associated antigen (MAA) genes and gene expression in melanomas of dogs.
Animals—18 dogs with malignant melanomas and 8 healthy control dogs.
Procedures—cDNA was prepared from malignant melanoma biopsy specimens and from pigmented oral mucocutaneous tissues of healthy control dogs. Genomic DNA was extracted from poorly pigmented melanomas. A PCR assay was performed by use of Melan-A, SILV, or tyrosinase-specific primers.
Results—Splice variants of Melan-A and SILV were identified in malignant melanomas and also in healthy pigmented tissues, whereas a tyrosinase splice variant was detected in melanoma tissues only. A short interspersed nuclear element (SINE) insertion mutation was identified in the SILV gene in 1 of 10 poorly pigmented melanomas. Six novel exonic single nucleotide polymorphisms (SNPs; 3 synonymous and 3 nonsynonymous) were detected in the tyrosinase gene, and 1 nonsynonymous exonic SNP was detected in the SILV gene.
Conclusions and Clinical Relevance—Variants of MAA mRNA were detected in malignant melanoma tissues of dogs. The importance of MAA alternative transcripts expressed in melanomas and normal pigmented tissues was unclear, but they may have represented a means of regulating melanin synthesis. The tyrosinase splice variant was detected only in melanomas and could potentially be a tumor-specific target for immunotherapy. A SILV SINE insertion mutation was identified in a melanoma from a Great Dane, a breed known to carry this mutation (associated with merle coat color). The nonsynonymous SNPs detected in tyrosinase and SILV transcripts did not appear to affect tumor pigmentation.
OBJECTIVE To compare outcomes of dogs treated surgically for oral, nontonsillar, squamous cell carcinomas (SCCs) and fibrosarcomas (FSAs) with outcomes of dogs treated with a combination of surgery and postoperative radiotherapy; to explore whether postoperative, hypofractionated radiotherapy improved outcomes of dogs with incomplete excisions; and to identify prognostic factors associated with outcome.
DESIGN Retrospective cohort study.
ANIMALS 87 client-owned dogs that had undergone maxillectomy or mandibulectomy for treatment of oral SCC or FSA between 2000 and 2009.
PROCEDURES Medical records were retrospectively reviewed. Survival analysis was performed with Kaplan-Meier and Cox regression analyses to evaluate potential prognostic factors associated with patient outcome.
RESULTS Median survival time (MST) for all 87 dogs was 2,049 days, but was not reached for dogs with SCC, and was only 557 days for dogs with FSA; tumor type was a significant predictor of survival time. Dogs undergoing postoperative radiotherapy after incomplete excision of oral SCCs had a significantly longer MST (2,051 days) than did dogs with incompletely excised tumors and no radiotherapy (MST, 181 days). Postoperative radiotherapy of dogs with incompletely excised FSAs did not appear to offer protective value (MST, 299 days with radiotherapy and 694 days without radiotherapy).
CONCLUSIONS AND CLINICAL RELEVANCE Wide-margin surgical excision should be considered the gold-standard treatment for dogs with oral SCC or FSA. For dogs with oral SCCs without clean surgical margins, survival times may be improved by providing postoperative, hypofractionated radiotherapy.