Mammary tumor
A mammary tumor is a
In dogs
Causes
The exact causes for the development of canine mammary tumors are not fully understood.
Biology
Historically, about 50 percent of mammary tumors in dogs were found to be malignant,
Malignant tumors are also subdivided histopathologically into those showing blood vessel wall invasion and those that do not. Without blood vessel wall invasion there is a better prognosis.[11] Dogs with noninvasive adenocarcinomas have an average survival time of two years, while dogs with invasive adenocarcinomas have an average survival time of one year.[11] Tumor size also affects the prognosis, in that dogs with tumors greater than five centimeters have a greater chance of lymph node metastasis.[12] Tumor type is also important. Sarcomas and carcinosarcomas carry an average survival time of nine to twelve months.[9] Inflammatory carcinomas have a very poor prognosis, and have usually metastasized by the time of diagnosis.[9] Metastasis for any malignant mammary tumor is usually to the regional lymph nodes and lungs.[11]
The molecular carcinogenesis of canine mammary tumors are not completely understood. However, the increasing information on molecular pathways involved in the carcinogenesis of this canine tumor has potential to complement and refine the current diagnostic and therapeutic approach to this tumor type.[5] Furthermore, current data show that significant similarities and differences exist between canine and human mammary tumors at the molecular level.[13][14]
Diagnosis and treatment
Appearance and location of the tumor is enough to identify it as a mammary tumor. Biopsy will give type and invasiveness of the tumor. In addition, newer studies showed that certain gene expression patterns are associated with malignant behaviour of canine mammary tumors.[5][13][14][15][16]
Surgical removal is the treatment of choice, but chest x-rays should be taken first to rule out metastasis. Removal should be with wide margins to prevent recurrence, taking the whole mammary gland if necessary. Because 40 to 50 percent of dog mammary tumors have estrogen receptors,[11] spaying is recommended by many veterinarians. A recent study showed a better prognosis in dogs that are spayed at the time of surgery or that had been recently spayed.[12] However, several other studies found no improvement of disease outcome when spaying was performed after the tumor had developed. Chemotherapy is rarely used.[4]
Breeds at increased risk
- Chihuahua
- Poodle
- Brittany Spaniel
- English Setter
- Pointer
- Fox Terrier
- Boston Terrier
- Cocker Spaniel[9]
- Lhasa Apso
In cats
Mammary tumors are the third most common neoplasia in cats, following lymphoid and skin cancers.[17] The incidence of mammary tumors in cats is reduced by 91 percent in cats spayed prior to six months of age and by 86 percent in cats spayed prior to one year, according to one study.[18] Siamese cats and Japanese breeds seem to have increased risk,[19] and obesity also appears to be a factor in tumor development.[20] Malignant tumors make up 80 to 96 percent of mammary tumors in cats, almost all adenocarcinomas.[21] Male cats may also develop mammary adenocarcinoma, albeit rarely, and the clinical course is similar to female cats.[22] As in dogs, tumor size is an important prognostic factor, although for tumors less than three centimeters the individual size is less predictive. According to one study, cats with tumors less than three cm had an average survival time of 21 months, and cats with tumors greater than three cm had an average survival of 12 months.[17] About 10 percent of cat mammary tumors have estrogen receptors, so spaying at the time of surgery has little effect on recurrence or survival time.[11] Metastasis tends to be to the lungs and lymph nodes, and rarely to bone.[23] Diagnosis and treatment is similar to the dog. There is a better prognosis with bilateral radical surgery (removing both mammary chains) than with more conservative surgery.[24] Doxorubicin has shown some promise in treatment.[25]
In rats
Most mammary tumors in rats are benign fibroadenomas, which are also the most common tumor in the rat.[26] Less than 10 percent are adenocarcinomas.[27] They occur in male and female rats. The tumors can be large and occur anywhere on the trunk.[28] There is a good prognosis with surgery.[29] Spayed rats have a decreased risk of developing mammary tumors.[30]
In mice
Most mammary tumors in mice are adenocarcinomas. They can be caused by viral infection.[27] Recurrence rates are high, and therefore there is a poor prognosis. There is frequently local tissue invasion and metastasis to the lungs.[28] A well known tumor virus of the mouse is the mouse mammary tumor virus, which may be the most common cause of this tumor in mice.[31]
In other animals
- Ferrets: Mammary tumors are rare in ferrets. Appearance tends to be a soft, dark colored lump. Most seem to be benign and occur most frequently in neutered males. Surgery is recommended.
- Guinea pigs: Mammary tumors in guinea pigs occur in males and females. Most are benign, but 30 percent are adenocarcinomas.[27] They usually do not metastasize, but aggressive surgery is necessary to prevent recurrence.
- Hamsters and gerbils: Mammary tumors tend to be benign in gerbils.[citation needed]
- Hedgehogs: Mammary gland adenocarcinoma is the most common tumor of the hedgehog.[26]
References
- ^ a b "Mammary Tumors: Introduction". The Merck Veterinary Manual. 2006. Retrieved 2007-03-21.
- PMID 10490210.
- ^ a b "Determining The Best Age At Which To Spay Or Neuter". 2008. Archived from the original (PDF) on 2015-12-08. Retrieved 2010-12-22.
- ^ a b Kirpensteijn, Jolle; Rutteman, Gerard R. (2006). "Practical treatment of mammary neoplasia" (PDF). Proceedings of the North American Veterinary Conference. Archived from the original (PDF) on 2007-09-29. Retrieved 2007-03-21.
- ^ PMID 21149845.
- ^ PMID 9598580.
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- ^ Sirivaidyapong, S. (2003). "Dogs with Mammary Gland Tumors and the Feeding Dietary Types". Proceedings of the 28th World Congress of the World Small Animal Veterinary Association. Retrieved 2007-03-21.
- ^ ISBN 978-0-7216-6795-9.
- ^ Nieto, Ana; Peña, Laura; Silvan, Gema; Perez-Alenza, Maria Dolores; Illera, Juan Carlos (2002). "Serum Hormone Profile of Canine Inflammatory Carcinoma". Proceedings of the 27th World Congress of the World Small Animal Veterinary Association. Retrieved 2007-03-21.
- ^ ISBN 978-0-683-06105-5.
- ^ PMID 16313041.
- ^ PMID 20932060.
- ^ PMID 21062462.
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- ^ PMID 11802667.
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- ^ Moore, Anthony (2004). "Advances in the treatment of mammary neoplasia" (PDF). Proceedings of the 31st World Congress of the World Small Animal Veterinary Association. Retrieved 2007-03-21.
- ^ PMID 15296867.
- ^ ISBN 978-0-7216-4023-5.
- ^ a b "Rats and Mice: Neoplasia". The Merck Veterinary Manual. 2006. Retrieved 2007-03-21.
- ^ Pritchett, K.R.; Corning, B.F. (2006). "Biology and Medicine of Rats". Laboratory Animal Medicine and Management. Archived from the original on 2009-02-12. Retrieved 2007-03-21.
- ^ Capello, Vittorio (2006). "Clinical and surgical approach to common diseases of pet rodents" (PDF). Proceedings of the North American Veterinary Conference. Retrieved 2007-03-21.
- PMID 16276516.