Feline 'Other' Tumors of Skin and Subcutis

Melanocytic tumors

Vet Pathol 33:1 31-38

Cutaneous melanomas are mostly malignant
spindle, epithelioid, mixed cell type are most common
signet ring and balloon type are rare, amelanotic and often look like carcinomas
Found on head mostly
S100 +, Vimentin +, NSE +, some desmin +
Human markers do not work
Tyrosinase specific mRNA is specific.
Mean life expectancy - 4.5 months (1 to 18 months)
Mets to Ln and other tissues - lung. Mets may be of another histological type.

Vet Derm 4: 19

43 cases
Head most often affected
Eyelids, lip malignant, ear benign
28 benign - symmetrical, well circumscribed,
15 malignant - giant cells high mitotic rate, dermal infiltration,

Vet Pathol  39: 127-132

Melan A stained 67% of 48 but is more specific (the only other tumor stained was sebaceous adenoma)
S100 stained 88% but is less specific.

Hirz M, Herden C. Cutaneous amelanotic signet-ring cell malignant melanoma with interspersed myofibroblastic differentiation in a young cat. J Vet Diagn Invest. 2016; 28: 429-435.

Signet ring type – large round cells with central protein and peripheral nucleus.
Signet ring cells (‘Rhabdoid”) were weak and rarely positive for Melan A and PNL2. Strongly positive for S100
Spindle cell component was SMA positive

 

 

The term 'melanocytic tumor' is one I wholeheartedly support. It is time to put the binary designation of benign and malignant "In The Bin". We are stuck with melanocytoma and malignant melanoma for the time being.

Pittaway et al (2019) published a large study of melanocytic tumors in cats that were those not in the eye. Their cases include those of the skin, nasal planum nasal mucosa oral and conjunctiva, and prepuce. Of the 324 animals, they had histology for 141 tumors and followup on 74.

• Locations were in ear (25%), head (20%), oral (17%) trunk (10%), nose (4%), lip (4%), conjunctiva/3rd eyelid (1%).
• Epithelioid were 57%, Spindle were 7%, mixed were 7%, and baloon cell (1.4%).
• Intravascular tumor was seen in 6 of the 141, and 3 were in the oral cavity.
• 42 of 80 died of tumor related causes with a median of 244.
• Individual predictors of survival were
  • tumor location - lip, oral, nasal were worst
  • mitotic count 4 or more per 10HPF worst
  • tumor necrosis presence worst.
  • Called high grade if there was one or more of these.
• IHC - all but 1 of 24 were positive for either PNL2 or Melan A
• Called high grade if

 

 

Pittaway R, Dobromylskyj MJ, Erles K, Pittaway CE, Suárez-Bonnet A, Chang YM, Priestnall SL. Nonocular Melanocytic Neoplasia in Cats: Characterization and Proposal of a Histologic Classification Scheme to More Accurately Predict Clinical Outcome. Vet Pathol. 2019; 56: 868-877.

Tactile epithelial (Merkle) cell tumor (carcinoma)

A tactile epithelial cell tumor (also called Merkel Cell Carcinoma) is a rare tumor of skin in cats. Tactile epithelial (Merkel) cells are of a neuroendocrine type. They are identified by amass extending from the epidermis, with an epithelial appearance but with distinct packeting.

Immunohistochemically, these stain with cytokeratins (especially CK 18, 19, 20), synaptophysin and chromogranin.

Ito et al (2022) examined Merkel Cell Carcinoma for Felis catus papillomavirus (FcaPV) and 20 of 21 were positive.

Ito et al (2023) further evaluated FcaPV2 oncogenes. This is the same papillomavirus involved with viral plaques, squamous cell carcinoma and basal cell carcinoma in cats. This study provides additional information supporting a causative role of the virus for this tumor.

 

 

 

 

Ito S, Chambers JK, Mori C, Sumi A, Omachi T, Nakayama H, Uchida K. Comparative In Vitro and In Vivo Studies on Feline, Canine, and Human Merkel Cell Carcinoma. Vet Pathol. 2021; 58: 276-287.

Ito S, Chambers JK, Sumi A, Yamashita-Kawanishi N, Omachi T, Haga T, Nakayama H, Uchida K. Involvement of Felis catus papillomavirus type 2 in the tumorigenesis of feline Merkel cell carcinoma. Vet Pathol. 2022 Jan;59: 63-74.

Ito S, Chambers JK, Sumi A, Omachi T, Haritani M, Nakayama H, Uchida K. Genomic integration and expression of Felis catus papillomavirus type 2 oncogenes in feline Merkel cell carcinoma. Vet Pathol. 2023; 60: 21-34.