A 14-year-old 54-kg (119-lb) spayed female Vietnamese potbellied pig (pig 1) was referred to the James L. Voss Veterinary Teaching Hospital at Colorado State University for evaluation of a draining tract of the cranial abdomen of unknown duration. A pyloric emptying disorder had been diagnosed in the pig 2 years previously, but the pig did not have clinical signs associated with abnormal pyloric emptying when examined at the teaching hospital. Ultrasonographic examination of the abdomen revealed a well-marginated, thick-walled structure extending from the abdominal wall to the liver parenchyma. Within the liver parenchyma, an enlarged area with a hypoechoic to anechoic center was detected. The center of the area appeared to swirl when ballottement was performed and had increased blood flow at its periphery, compared with blood flow elsewhere within the adjacent parenchyma. The gall bladder could not be identified. A presumptive diagnosis of liver abscess with a cutaneous draining tract was made, and surgical removal was planned for 1 week later. Hematologic and biochemical abnormalities detected at the time of this initial evaluation included anemia (PCV, 23%; reference limits, 32% to 50%) and hyperglobulinemia (serum globulins concentration, 4.2 g/dL; reference limits, 1.5 to 3.5 g/dL).
The following week, the pig was returned for surgery. A celiotomy was performed via a routine ventral midline approach to the abdomen, revealing a fibrous mass measuring approximately 15 × 5 cm, which was adhered to the body wall at the site of the draining tract and extended through the liver. Grossly normal gall bladder tissue could not be identified. The cystic duct was ligated at the site of its attachment to the mass. The mass was removed in its entirety with wide (ie, 3-cm) margins and submitted for histologic evaluation. The remainder of the abdomen was explored, and no additional abnormalities were detected with the exception of a mild thickening of the pylorus. The pig recovered well from anesthesia and was discharged from the hospital the day after surgery. Postoperative vomiting developed but was controlled with metoclopramide (0.2 mg/kg [0.09 mg/lb], PO, q 12 h) and small feedings; the vomiting resolved 2 days later.
Histologic evaluation of the gall bladder revealed a mass of closely packed to loosely arranged clusters and acini of neoplastic gall bladder epithelial cells that infiltrated the surrounding tissue (Figure 1). Marked proliferation of dense fibrous connective tissue appeared to have developed around the mass. The adjacent liver had evidence of diffuse collapse of lobules with dense fibrous tissue. The final diagnosis was cholangiocellular carcinoma and moderate diffuse chronic cholangiohepatitis. Surgical margins were not evaluated.
Photomicrographs of a tissue section from a cholangiocellular carcinoma detected in a Vietnamese potbellied pig (pig 1). A—The tumor involves nearly the entire mucosa and has infiltrated into the submucosa. H&E stain; bar = 500 μm. B—Magnification (10X) of the tissue in the boxed area in panel A. This region of tissue is comprised nearly entirely of neoplastic cells with marked anisocytosis and anisokaryosis. Mixed inflammatory cells are also evident at the bottom of the image. Bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 235, 11; 10.2460/javma.235.11.1336
A follow-up ultrasonographic examination of the liver was performed 8 months after surgery. At that time, there was no evidence of additional neoplastic nodules, and the overall size of the liver was unremarkable. The pig was judged systemically healthy, although the owner reported it was intolerant of foods containing a high concentration of fat and had lost approximately 2.3 kg (5 lb) since the surgery. Although the pig was evaluated 3 additional times because of signs of inappetence and lethargy (64, 82, and 84 months after surgery), a diagnosis of small intestinal disease was made, and the condition improved after treatment with a combination of antimicrobials (amoxicillin; 7.5 to 10 mg/kg [3.5 to 4.5 mg/lb], PO, q 12 h), anti-inflammatory drugs (prednisone; 0.4 mg/kg [0.2 mg/lb], PO, q 12 h), prokinetic agents (cisapride; 0.1 mg/kg [0.045 mg/lb], PO, q 12 h), and antiemetic drugs (metoclopramide; 0.2 mg/kg, PO, 30 minutes before meals). Eighty-five months after surgery, the pig was returned to the teaching hospital for evaluation for a 3-day history of anorexia and oral and nasal hemorrhage that had worsened during the previous 24 hours. Immune-mediated thrombocytopenia was suspected, but diagnostic testing was not pursued. The owner elected to euthanize the pig and declined a necropsy.
A second Vietnamese potbellied pig (16 years old; 45 kg [99 lb]; pig 2) was evaluated for a 2-week history of diarrhea, vomiting, anorexia, and dehydration. The pig's condition had improved somewhat after treatment at home with orally administered fluids, but on the day of evaluation, it had become weak and could not stand. Initial physical examination revealed dehydration (estimated at 10%), pale mucous membranes with a capillary refill time > 3 seconds (reference limit, < 2 seconds), and a rectal temperature of 36.1°C (97°F). A firm mass was palpated in the midabdomen, and ultrasonographic examination revealed the mass was homogenous, multilobulated, and surrounded by free fluid of mixed echogenicity. Abdominocentesis yielded frank blood. Hematologic abnormalities detected during the initial evaluation included anemia (PCV, 18%) and leukocytosis (23.2 × 103 WBCs/μL; reference limits, 11.0 × 103 WBCs/μL to 22.0 103 WBCs/μL) with a regenerative shift to the left (19 × 103 segmented neutrophils/μL, 900 band cells/μL, and 500 metamyelocytes/μL).
An emergency exploratory celiotomy was performed on the basis of results from the clinical evaluation. The immediate surgical finding was copious free blood and an enlarged and ruptured spleen, which was removed with the aid of a stapling device.a Because of extensive blood loss from the ruptured spleen, a bovine hemoglobin productb was administered (10 mL/kg, IV). The abdomen was thoroughly lavaged following removal of the spleen, and the remainder of the abdomen was routinely explored. A mass was palpated in the gastric fundus near the pylorus. Gastrotomy revealed a well-circumscribed soft tissue mass that was 3 cm in diameter and attached to the gastric mucosa by a vascular pedicle that was 0.5 cm in diameter. The mass was removed at its attachment with the aid of a stapling device,a and the gastrotomy incision was routinely closed. The remainder of the gastrointestinal tract was unremarkable. The gastric mass and multiple specimens obtained from the spleen were submitted for histologic evaluation. A CBC performed before the pig was discharged from the hospital (5 days after surgery) revealed a platelet count within reference limits and a strong regenerative response to anemia. At that time, the pig was eating, drinking, urinating, and defecating unremarkably.
Histologic evaluation of the gastric mass revealed a highly infiltrative, poorly demarcated mass composed of ill-defined acini and tubular structures as well as lobules and nests of pleomorphic epithelial cells embedded within fibrous connective tissue (Figure 2). Neoplastic cells extended transmurally individually and in small nests from the mucosa to the muscularis and were also detected within blood vessels. Supporting stroma contained marked lymphocyte infiltration. These findings were consistent with a transmural gastric carcinoma with metastasis to the local vasculature. No evidence of neoplasia was detected in spleen specimens.
Photomicrograph of a tissue section from a gastric carcinoma detected in a Vietnamese potbellied pig (pig 2). Lobules and nests of neoplastic cells embedded within fibrous connective tissue fill most of the tissue section (arrow). Although neoplastic cells were detected within blood vessels in this pig, that characteristic is not evident in this section.
Citation: Journal of the American Veterinary Medical Association 235, 11; 10.2460/javma.235.11.1336
The pig was not returned to the teaching hospital for a follow-up examination; however, the owner was contacted by telephone 24 months after surgery. At that time, the pig was reportedly healthy with no evidence of tumor recurrence or metastasis.
A 12-year-old 42-kg (92.4.-lb) sexually intact female Vietnamese potbellied pig (pig 3) was evaluated because of a 1-month history of a lower than typical appetite and a 1-week history of anorexia. The pig had been vomiting 1 to 2 times/wk during the month preceding the evaluation and had a 1-year history of weekly seizures. No specific treatments had been administered by the owners for either condition.
During the initial examination, the pig had a grand mal seizure of approximately 60 seconds in duration. A CBC and serum biochemical analysis were performed, revealing an unremarkable total WBC count with a shift to the left (800 band cells/μL). A mild anemia was also evident (PCV, 29%) as well as a mild increase in serum activity of alanine aminotransferase (105 U/L; reference limits, 23 to 83 U/L).
Abdominal radiographs revealed a distended stomach filled with fluid and gas and at least 2 segments of severely gas-distended small intestine. Most of the small intestine and colon appeared to be unremarkable in dimension but were displaced caudally and dorsally by the distended segments. These findings were interpreted as consistent with a partial bowel obstruction, and treatment with metoclopramide (0.4 mg/kg, IV, q 8 h) and cisapride (0.5 mg/kg [0.23 mg/lb], PO, q 8 h) was initiated to promote gastrointestinal motility. Intravenous administration of fluidsc (150-mL bolus, q 2 h) was also initiated, as was treatment with ceftiofur (4.4 mg/kg [2 mg/lb], IV, q 12 h). Several warm water and soap enemas were administered. Two additional, less severe seizures were observed during hospitalization; however, the pig recovered from all seizures without treatment, and the cause of the condition was not pursued at the owner's request. The dose of metoclopramide was reduced to 0.2 mg/kg after 24 hours because of concern that the high dose initially administered was lowering the pig's seizure threshold. During 3 days of hospitalization, the pig's condition improved. Radiographs obtained 3 days after admission revealed that the gastric distention had resolved and the small intestinal distention had improved but not resolved. Because the pig was responding to medical treatment while hospitalized, exploratory celiotomy was not pursued. The prognosis was deemed fair, depending on continued response to treatment.
Three days after discharge from the hospital, the pig was euthanized at home because of worsening of clinical signs, including increased frequency and severity of seizures, and was returned for postmortem examination. The examination revealed a firm, white mass that was 1.5 cm in diameter protruding into the lumen of the distal jejunum and obstructing approximately 90% of the jejunum's diameter. Oral to the mass, the jejunum was moderately distended. The brain and brainstem appeared grossly unremarkable. Results of the necropsy and subsequent histologic evaluation of the mass were consistent with a diagnosis of small intestinal adenocarcinoma.
A 15-year-old 46-kg (101.2-lb) castrated male Vietnamese potbellied pig (pig 4) was evaluated for a neck mass of 2 months' duration and an abdominal mass of > 3 years' duration. The owner had previously declined diagnostic investigation of the abdominal mass. Results of a physical examination at the hospital were unremarkable, although the pig was judged thin and the owner reported gradual weight loss during the preceding few weeks to months. Palpation of the throat revealed no abnormalities. During palpation of the abdomen, a large, firm, multilobulated mass was detected in the cranial abdomen. Ultrasonographic evaluation revealed the mass had mixed echogenicity with some cystic structures and areas of mineralization. These findings suggested the mass arose from the liver.
Similar to findings in the other pigs, results of a CBC indicated leukocytosis with a shift to the left. Serum biochemical analysis revealed hyperproteinemia (total protein concentration, 9.7 g/dL; reference limits, 6 to 8 g/dL), hyperglobulinemia (globulins concentration, 6.4 g/dL), mild hyperbilirubinemia (total bilirubin concentration, 0.5 mg/dL; reference limit, < 0.3 mg/dL), and mild hypokalemia (3.2 mEq/L; reference limits, 3.9 to 5.9 mEq/L). In addition, the serum concentration of bile acids was remarkably high (73 μmol/L; no reference limit for pigs available; reference limit for dogs, < 6 μmol/L; reference limit for horses, < 15 μmol/L).
An attempt was made to obtain biopsy specimens of the mass; however, the specimens obtained were unusable for diagnostic purposes. Because of the duration of the mass and a concern that it was neoplastic and might have metastasized, survey radiographs of the lungs were obtained, revealing a diffuse, nodular, interstitial pattern throughout the pulmonary parenchyma as well as multiple discrete nodules of soft tissue opacity, the largest measuring 18 mm in diameter (Figure 3). The size of the pig allowed for evaluation of the cranial abdomen on the same films. The liver appeared large, with multiple well- to ill-defined partially mineralized nodules within the parenchyma. These findings were considered to be most consistent with a primary liver tumor with pulmonary metastasis. Consequently, the owner elected to take the pig home to live out the remainder of its life. Six days after discharge from the hospital, the pig died and was returned for necropsy. Results of the necropsy and subsequent histologic evaluation of the mass and lung nodules were consistent with a diagnosis of metastatic hepatocellular carcinoma.
Thoracic radiograph (right lateral view; head is toward the left) of a Vietnamese potbellied pig (pig 4) revealing metastasis of a hepatocellular carcinoma throughout the lungs. Discrete nodules of soft tissue opacity measuring up to 18 mm in diameter can be seen (arrowheads). Mineralized nodules within the primary liver mass are also evident (arrow).
Citation: Journal of the American Veterinary Medical Association 235, 11; 10.2460/javma.235.11.1336
An 11-year-old 36-kg (79.2-lb) spayed female Vietnamese potbellied pig (pig 5) was evaluated at the teaching hospital for a 7-day history of failure to defecate. Treatment with metoclopramide was initiated at home with no improvement. Two months previously, the pig had 6 teeth extracted; since that time, it had signs of inappetence and mild constipation. Warmwater enemas and orally administered mineral oil had resolved the mild constipation until 1 week prior to admission to the teaching hospital. The pig had a history of 2 abdominal surgeries: an elective spay at < 6 months of age and an emergency exploratory celiotomy after evaluation for signs of acute abdominal pain and a rectal prolapse at 1 year of age.
Physical examination revealed the pig was bright, alert, and responsive. Abdominal radiographs revealed marked gaseous distention throughout the gastrointestinal tract, with cranioventral displacement of the cecum. Treatment was initiated with isotonic fluidsc (3.3 mL/kg/h [1.5 mL/lb/h], IV), famotidine (1 mg/kg [0.45 mg/lb], IV, q 12 h), cisapride (0.5 mg/kg, PO, q 8 h), and metoclopramide (0.4 mg/kg, PO, q 12 h), but when abdominal radiographs were obtained 24 hours later, they revealed no improvement in the appearance of the gastrointestinal tract. An exploratory celiotomy was consequently recommended. Results of a preoperative hematologic analysis were unremarkable except for a mild anemia (PCV, 29%).
During surgery, multiple adhesions were evident between the body wall and the spiral colon, some of which involved the simple, continuous line of nylon sutures remaining from the exploratory surgery performed 10 years earlier. Additional exploration revealed a grossly enlarged spleen and markedly gas-distended loops of bowel, which started in the midjejunum and extended into the spiral colon. A 5 × 5-cm mass was palpated between 2 loops of spiral colon, at the junction between the centrifugal and centripetal loops; it appeared to have caused stenosis of the colon and chronic dilation of the oral segment. This mass was deep to and intimately associated with the mesentery of the spiral colon. Consequently, the affected loops of spiral colon and the mass were resected en bloc (Figure 4). A side-to-side anastomosis of the spiral colon was performed with the aid of stapling equipment.d,e The only other remarkable finding during the exploratory surgery was a mottled appearance of the spleen.
Gross appearance of the excised mass and loop of spiral colon in pig 5. The mass was deep to and intimately associated with the colonic mesentery (location is indicated with the oval). The mass was identified histologically as a lymph node with its normal architecture effaced by neoplastic cells, likely of colonic origin.
Citation: Journal of the American Veterinary Medical Association 235, 11; 10.2460/javma.235.11.1336
Punch-biopsy specimens were obtained from the spleen and were later submitted along with the colon mass for histologic evaluation. The pig was discharged from the hospital 3 days after surgery. Histologic evaluation of the mass revealed it was a lymph node with typical lymph-node architecture effaced by neoplastic cells arranged in small nests and acini. The encapsulated mass was surrounded by abundant granulation tissue with a moderate number of lymphocytes. There were no histologic abnormalities within the resected loop of spiral colon. The neoplastic mass was morphologically consistent with an adenocarcinoma of gastrointestinal origin, but no definitive cell of origin could be identified. A final diagnosis of carcinoma with marked desmoplasia was made. There was no evidence of neoplastic cells in the spleen biopsy specimen.
Although the pig was not returned to the teaching hospital for a follow-up examination, the owner was contacted by telephone 9 months after surgery. At that time, the pig was reportedly healthy, with no evidence of tumor regrowth or metastasis.
Discussion
Neoplasia of gastrointestinal or hepatobiliary origin in pigs is infrequently reported, and most of the reports1–7 concern domestic breeds in which the lesions were detected at slaughter or as incidental findings at necropsy. To our knowledge, alimentary-associated tumors in Vietnamese potbellied pigs have not been reported. This breed represents a small but important portion of pet livestock patients in many practices, and there is little published information regarding the incidence or clinical manifestations of neoplasia of any type in this population. We report 5 geriatric Vietnamese potbellied pigs with alimentary-associated carcinoma or adenocarcinoma, which were evaluated at our hospital between January 2000 and June 2008. These pigs represented 1% of the total potbellied pigs evaluated at our hospital during this period (total of 438 visits in 8 years) and 12% of pigs that were evaluated for nonspecific signs of abdominal distress.
The most commonly reported types of neoplasms in domestic pigs are lymphoma, melanoma, and embryonal nephromas, but even these types are uncommonly detected in large abattoir or diagnostic laboratory surveys.2,3,6,7 One survey3 of federally inspected slaughter facilities resulted in the identification of tumors in 28 domestic pigs during a 2-year period. Of these, 13 tumors were embryonal nephromas, 9 were lymphomas, and 3 were melanomas. A similar 5-year survey2 resulted in the identification of tumors in 32 pigs, including 11 embryonal nephromas and 12 lymphomas (data on melanoma detection were excluded).2 Overall incidences of tumor detection in the 2 aforementioned surveys were 1/35,000 pigs2 and 1/25,000 pigs,3 respectively. By comparison, the incidence of tumor detection in cattle in the first survey2 was 1/1,500 cattle, even when data on detection of ocular squamous cell carcinoma, the most commonly identified tumor in cattle at slaughter during the survey period, were excluded.3 In neither of these abattoir surveys were tumors of the liver or intestines identified. It has been suggested that the reason for the low incidence of neoplasia in pigs is that most are slaughtered before they reach geriatric age, but to our knowledge, this hypothesis has never been objectively evaluated. In the United States, Vietnamese potbellied pigs are considered companion animals and therefore live long enough to develop diseases associated with advancing age.
A few reports of neoplasia in Vietnamese potbellied pigs exist, including 2 pigs with uterine leiomyomas8; 1 pig with metastatic endometrial adenocarcinoma9; 1 pig with metastatic oral squamous cell carcinoma, uterine adenocarcinoma, and hepatocellular adenoma10; and 1 pig with hepatocellular carcinoma and suspected splenic hemangiosarcoma.11 The aforementioned pigs ranged in age from 8 to 16 years at the time of diagnosis. The youngest pig in the present clinical report was 11 years old. These findings support the supposition that neoplasia emerges as an important disease in Vietnamese potbellied pigs of middle to old age.
Primary liver tumors in domestic pigs have been reported only rarely, although lymphoma of the liver as a secondary or metastatic tumor is fairly common.4,12 Aflatoxins fed at 1 ppm reportedly cause liver cancer in pigs,13 but there was no evidence of exposure to any toxicants in the pig with hepatocellular carcinoma reported here. An abattoir study4 of tumors in pigs resulted in the identification of primary liver-cell tumors in 4 of 139 (2.9%) tumors. Two of the tumors were detected in pigs < 6 months of age, and the other 2 were detected in adult pigs. Three of the 4 lesions appeared to be solitary, although multiple neoplastic nodules were detected in the liver of 1 adult pig.4 Solitary, well-differentiated hepatocellular carcinomas have also been detected in a 6-month-old male domestic pig5 and a 10-year-old male castrated Vietnamese potbellied pig.11 In none of the aforementioned pigs were metastases detected. In contrast, metastases to the local lymph nodes, spleen, peritoneum, omentum, endocardium, and lungs were detected in a 2-year-old large white Yorkshire sow in which primary hepatocellular carcinoma had been diagnosed.14 These findings are similar to those in pig 4 of the present report, in which multiple neoplastic nodules were detected in the lungs. The proportion of hepatocellular carcinomas that result in metastases in other animal species ranges from 25% to 61%.13 It is possible that pigs have a similar likelihood of developing metastatic hepatocellular carcinomas, although additional research is needed to evaluate that likelihood. It is impossible to determine whether early surgical intervention would have prolonged the life of pig 4, but in dogs, survival for 1 year is possible after surgical removal of affected liver lobes.13
To our knowledge, there has been only 1 other report4 of a gallbladder tumor in a pig. That pig, a 3-year-old domestic sow, developed a tumor involving much of the mucosa of the gall bladder; the diagnosis was papillary adenocarcinoma.4 In contrast, the tumor that developed in pig 1 in the present report was identified as cholangiocellular carcinoma, but was not papillary. No metastases were evident at the time of surgery in pig 1, and excision was curative, with the pig surviving 7 years after surgery. Although a necropsy was declined, the clinical signs that ultimately led to euthanasia of that pig were not consistent with those of the original neoplastic disease, and the 2 conditions were not likely related.
Although in the present report we describe 3 primary intestinal tumors, such tumors have otherwise been only rarely reported. Gastric carcinomas, such as that described in pig 2, are most common in dogs, but an affected domestic pig has been reported.15 In contrast to humans, in whom gastric ulceration caused by Helicobacter pylori has been linked to an increased risk of gastric carcinoma,16 there does not seem to be a similar link between gastric-ulcer disease and malignant neoplasia in pigs.15 Although there was microscopic evidence of transmural metastasis with vascular invasion in pig 2, the pig survived for at least 2 years after surgery, with no evidence of local recurrence or distant metastasis of the tumor. This finding is similar to the survival rate in dogs with surgically removed gastric carcinomas (12 to 35 months).15
Adenocarcinoma of the small intestine in pigs has only been investigated in 1 survey1 of intestinal tumors detected at slaughter. In that survey, 5 domestic sows had tumors that were located in the middle or distal third of the jejunum and were annular, leading to stenosis of the intestine at the affected site. In 3 of the pigs, the tumors had metastasized to the regional lymph nodes, and in 1 of those 3, distant metastases were detected in the lungs. The tumor detected in pig 3 of the present report was similar to tumors detected in the survey1 in that it was located in the distal jejunum and protruded into the lumen, causing obstruction. However, there was no evidence of metastasis in pig 3. No report of excision of this type of tumor in a pig exists, but in dogs, tumor redevelopment at the site of anastomosis and development of distal metastases in previously unaffected organs are reportedly common.15
The tumor detected in pig 5 of the present report was classified as an undifferentiated carcinoma but had features consistent with an adenocarcinoma. Given its location, the tumor was most likely of colonic origin. Colorectal carcinomas, although among the most common human types of cancer in some parts of the world,17 are rarely identified in veterinary species. However, among domestic animal species, dogs are most commonly affected with this type of tumor, and it has been hypothesized that this may be attributable to the fact that dogs share an environment that may expose them to the same carcinogens as humans.17 To our knowledge, no colorectal carcinomas in pigs have been reported, but there is a report1 of a sow with a well-demarcated mucoid adenocarcinoma of the cecum that metastasized to a regional lymph node and lungs. In the pig of the present report, no evidence of metastasis was detected during surgery, and the mass was removed in its entirety by resecting a loop of the spiral colon. Subtotal colectomy and spiral-colon bypass procedures in Vietnamese potbellied pigs have been described,18,19 but to our knowledge, this is the first time that use of a side-to-side resection and anastomosis of the spiral colon has been reported. The technique used was an adaptation of that described for removing the large colon in horses20 and allowed bypass of the affected loops of spiral colon without the need for extensive dissection of the mesentery.
Although neoplasia is generally considered rare in pigs, it should not be overlooked in the differential diagnosis of generalized abdominal distress in middle-aged and older Vietnamese potbellied pigs. As was evident in the pigs of this report, tumors can potentially arise from multiple components of the gastrointestinal and hepatobiliary tracts, including the liver, gall bladder, stomach, small intestine, and spiral colon. If neoplasia is suspected, tumor excision may provide a good outcome. All 3 pigs that were treated surgically survived at least 9 months after surgery with good quality of life. Additional research is needed to determine the metastasis rate of each type of tumor and survival rates for affected pigs, but our limited experience has indicated that early intervention can and should be attempted in these situations, with a reasonable expectation of a positive outcome.
LDS, Kendall Animal Health, Mansfield, Mass.
Oxyglobin, Biopure Corp, Cambridge, Mass.
Normosol-R, Abbot Laboratories, Abbott Park, Ill.
ILA 100, Kendall Animal Health, Mansfield, Mass.
TA 90, Kendall Animal Health, Mansfield, Mass.
References
- 1.↑
Vítovec J. Carcinomas of the intestine in cattle and pigs. Zentralbl Veterinarmed A 1977;24:413–421.
- 3.↑
Monlux AW, Anderson WA, Davis CL. A survey of tumors occurring in cattle, sheep, and swine. Am J Vet Res 1956;17:646–677.
- 4.↑
Anderson LJ, Sandison AT. Tumors of the liver in cattle, sheep, and pigs. Cancer 1968;21:289–301.
- 5.↑
Bundza A, Greig AS, Dukes TW. Primary hepatocellular carcinoma in animals killed at meat packing plants: report of 11 cases. Can Vet J 1984;25:82–85.
- 6.
Cotchin E. Tumors of farm animals: a survey of tumors examined at the Royal Veterinary College, London, during 1950–60. Vet Rec 1960;40:816–822.
- 7.
Fisher LF, Olander HJ. Spontaneous neoplasms of pigs—a study of 31 cases. J Comp Pathol 1978;88:505–517.
- 8.↑
Munday JS, Stedman NL. Uterine leiomyomas in two Vietnamese pot-bellied pigs (Sus scrofa). Vet Pathol 2002;39:580–583.
- 9.↑
Harmon BG, Munday JS, Crane MM. Diffuse cystic endometrial hyperplasia and metastatic endometrial adenocarcinoma in a Vietnamese pot-bellied pig (Sus scrofa). J Vet Diagn Invest 2004;16:587–589.
- 10.↑
Kleinschmidt S, Puff C, Baumgärtner W. Metastasizing oral squamous cell carcinoma in an aged pig. Vet Pathol 2006;43:569–573.
- 11.↑
Morrow JL. Hepatocellular carcinoma and suspected splenic hemangiosarcoma in a potbellied pig. Can Vet J 2002;43:466–468.
- 12.
Stalker MJ, Hayes MA. Liver and biliary system. In: Maxie MG, ed. Pathology of domestic animals. 5th ed. Edinburgh: Elsevier Ltd, 2007;382–388.
- 13.↑
Cullen JM, Popp JA. Tumors of the liver and gall bladder. In: Meuten DJ, ed. Tumors in domestic animals. 4th ed. Ames, Iowa: Iowa State University Press, 2002;483–504.
- 14.↑
Ramachandran KM, Rajan A, Mony G, et al. Hepatocellular carcinoma in a pig. Indian Vet J 1970;47:304–306.
- 15.↑
Head KW, Else RW, Dubielzig RR. Tumors of the alimentary tract. In: Meuten DJ, ed. Tumors in domestic animals. 4th ed. Ames, Iowa: Iowa State University Press, 2002;401–478.
- 16.↑
Jones TC, Hunt RD, King NW. Diseases caused by bacteria. In: Jones TC, Hunt RD, King NW, eds. Veterinary pathology. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 1997;434.
- 17.↑
Lingeman CH, Garner FM. Comparative study of intestinal adenocarcinomas of animals and man. J Natl Cancer Inst 1972;48:325–346.
- 18.
Bassett JR, Mann FA, Constantinescu GM, et al. Subtotal colectomy and ileocolic anastomosis in a Vietnamese pot-bellied pig with idiopathic megacolon. J Am Vet Med Assoc 1999;215:1640–1643.
- 19.
Gallardo MA, Lawhorn DB, Taylor TS, et al. Spiral colon bypass in a geriatric Vietnamese potbellied pig. J Am Vet Med Assoc 2003;222:1408–1412.
- 20.↑
Rakestraw PC, Hardy J. Large intestine. In: Auer JA, Stick JA, eds. Equine surgery. 3rd ed. St Louis: Saunders Elsevier, 2006;462–465.
