Cutaneous amelanotic signet-ring cell malignant melanoma with interspersed myofibroblastic differentiation in a young cat

Abstract

Abstract. The diagnosis of malignant melanoma can be difficult because these tumors can be amelanotic and may contain diverse variants and divergent differentiations, of which the signet-ring cell subtype is very rare and has only been described in humans, dogs, cats, and a hamster. We describe herein histopathologic and immunohistochemical approaches taken to diagnose a case of signet-ring cell malignant melanoma with myofibroblastic differentiation in a cat. A tumor within the abdominal skin of a 2-year-old cat was composed of signet-ring cells and irregularly interwoven streams of spindle cells. Both neoplastic cell types were periodic-acid-Schiff, Fontana, and Sudan black B negative. Signet-ring cells strongly expressed vimentin and S100 protein. Spindle cells strongly expressed vimentin and smooth muscle actin; some cells expressed S100, moderately neuron-specific enolase, and others variably actin and desmin. A few round cells expressed melan A, and a few plump spindle cells expressed melan A and PNL2, confirming the diagnosis of amelanotic signet-ring cell malignant melanoma with myofibroblastic differentiation in a cat. Differential diagnoses were excluded, including signet-ring cell forms of adenocarcinomas, lymphomas, liposarcomas, leiomyosarcomas, squamous cell carcinomas, basal cell carcinomas, and adnexal tumors.

What is your diagnosis? Skin mass in a cat

“…1,2 In four recent reports of feline melanomas, where the signet-ring morphology was specifically acknowledged, 15% (23/149) of the tumors exhibited this feature. [1][2][3][4] However, this overall rate of occurrence was biased by one report where 37% (21/57) of the tumors were of the signet-ring morphology, 1 while the two other multi-animal studies had much lower occurrences of 0% (0/23), 4 and 2% (1/48). 2 The single tumor in the latter report was sampled from the lung, which differed from the cutaneous origin in the report by Van Der Linde-Sipman et al 1,2 The signet-ring variant of melanoma can consist entirely of signet-ring cells but can also coincide with epithelioid-type cells, as was seen in 8/21 melanomas in one study.…”

“…In the current report, a small amount of melanin was focally concentrated in a few small groups of cells, which included both the signet‐ring and epithelioid types, and Melan A was positive in approximately ¼ of the neoplastic cells. In the two reports that performed Melan A IHC in signet‐ring type tumors of cats, there was negative staining in one and only isolated positive cells in the other 2,3 . Neither of these tumors had a reported epithelial component, nor was melanin pigment apparent.…”

“…Cutaneous malignant melanomas are uncommon in cats, with the epithelioid type being the most common histologic pattern, and the signet‐ring type being uncommon 1,2 . In four recent reports of feline melanomas, where the signet‐ring morphology was specifically acknowledged, 15% (23/149) of the tumors exhibited this feature 1‐4 . However, this overall rate of occurrence was biased by one report where 37% (21/57) of the tumors were of the signet‐ring morphology, 1 while the two other multi‐animal studies had much lower occurrences of 0% (0/23), 4 and 2% (1/48) 2 .…”

“…In the two reports that performed Melan A IHC in signet-ring type tumors of cats, there was negative staining in one and only isolated positive cells in the other. 2,3 Neither of these tumors had a reported epithelial component, nor was melanin pigment apparent. In 3 signet-ring type melanomas in dogs, only 1 case was Melan A positive, which also had epithelioid type cells and melanin present.…”

Atypical myopathy in 2 Bactrian camels

“…4). Immunohistochemistry using an anti-neurofilament antibody (Clone 2F11, dilution 1:400, Dako; blocking with horse serum, biotinylated horse anti-mouse IgG secondary antibody and ABC detection system, Vector) was performed on brachial nerve sections, as described previously, 9 showed homogeneous staining of nerve fibers, indicating no significant loss of axons.…”