Lumps, bumps, and skin masses are frequently encountered in feline medicine. These are often of major concern to cat owners as they are generally easily detectable and may cause obvious distress to the cat. Masses of the skin may be the result of infection, trauma, cancer, or other processes. Skin masses may be completely benign, but may also represent primary or metastatic malignancies. Previous studies have indicated that fibrosarcoma, basal cell carcinoma, mast cell tumor, and squamous cell carcinoma are the most common skin tumors of cats. Cancer is the cause of death of ¼ of cats in the UK, and 30-40% of cancers arise within the skin. Knowledge of the most common tumors and their age, sex, and breed predilections may allow for more appropriate diagnostics and targeted research into the most relevant diseases.
The purpose of this study was to utilize a large diagnostic laboratory database to assess the prevalence of various skin tumors in domestic cats, and their association with breed, sex, and age. Records of masses submitted for histopathology in the UK between 2006 and 2013 were reviewed. Tumors located within the skin (excluding mammary, oral cavity, and third eyelid) were included, along with those arising from the ear or anal gland. Breed, age, sex, neuter status, and histologic diagnosis were recorded. Masses were classified as neoplastic or non-neoplastic, with the neoplastic further subdivided by embryologic origin.
9683 samples were analyzed from 9200 cats of 35 breeds. This represented 4.4% of blood, biopsy, and histopathology samples to this lab. 89 separate diagnoses were recorded.
Of these masses, 6.6% were non-neoplastic in origin. Of the neoplastic masses, 47.6% were benign, and 52.7% were malignant. 5 masses could not be characterized as benign or malignant.
Of the benign neoplasms, epithelial origin were the most common, followed by mesenchymal, hematopoietic, and melanocytic. For malignancies, mesenchymal origin were more common, followed closely by epithelial, with metastatic, melanocytic, and hematopoetic much less common.
British Blue and Himalayan cats were more likely to develop a skin tumor than non-purebreds. Conversely, Siamese, Burmese, Birmans, and Oriental breeds were less likely to develop a skin mass. No breed was more likely to develop a malignant mass, however Persian, Siamese, Burmese, Ragdoll, British, Blue, Birman, and Norwegian Forest cats were less likely to be diagnosed with a malignancy. It must be remembered that these are in cats of UK origin - cats from other geographic regions and lines may have differing predispositions.
The median age of a cat was 11 years at diagnosis. Malignant tumors were more likely to occur in cats >12 years of age. Male neutered cats were more likely to develop benign masses at an earlier age, however no other associations with age and sex were seen.
The 10 most common skin tumors accounted for 80% of diagnoses. As previously reported, the most common were basal cell tumours, fibrosarcoma, squamous cell carcinoma, and mast cell tumor. These were followed by lipoma, hemangiosarcoma, apocrine cystadenoma, undifferentiated carcinoma, basal cell carcinoma, and ceruminous gland tumor.
Several breeds were found to have higher or lower rates of certain neoplasms, discussion of which is beyond the scope of this summary. Of particular note is the predilection of Siamese, Burmese, Russian Blue, Ragdoll, Maine Coon, Oriental and Havana breeds to mast cell tumors, and of the Persian to squamous cell carcinoma, fibrosarcoma, and basal cell tumor.
Some degree of sampling bias is present in this study, as masses with a lower index of suspicion for malignancy or responsive to therapy may have been be under-sampled. The exclusion of mammary masses is also likely to leave out many (likely malignant) skin masses due to the high prevalence of mammary neoplasia in cats. Location of origin was not recorded by authors, which may be a major factor influencing the type and prognosis of tumors.
This study provides a detailed look at the distribution of skin masses in a large number of cats in the UK. While its results are largely confirmatory of previous studies, the analysis of breed predilections may prove valuable. Of major note is that ~50% of skin masses were neoplastic malignancies, emphasizing the important of prompt diagnosis and intervention.
