Combined Merkel Cell Carcinoma and Atypical Fibroxanthoma

Abstract

This case is an interesting and unusual combination of tumors. The origin of the Merkel cell carcinoma is revisited. Debated origins include neuroendocrine, epithelial, and pleuripotent stem cell.

Merkel cell carcinoma with sarcomatous differentiation: is it a poor prognostic factor?

“…Poor prognostic factors include male sex, advanced stage at diagnosis, large tumor size (>5 mm), diffuse growth pattern, heavy lymphocytic infiltrate, and high mitotic rate 3 . In all cases of merkelomas with sarcomatous differentiation described to date, 1–6 lymph node metastases have been found, except in the presented case (Table 1). However, larger series of cases will be required to determine if sarcomatous differentiation represents another negative prognostic factor.…”

Merkel cell carcinoma with squamous and sarcomatous differentiation

“…Also, in the ontogenesis of human skin, Merkel cells appear first in the epidermis; some then migrate into the dermis 5 . It is possible that Merkel cell carcinoma arises not from the Merkel cell itself, but from an epidermal stem cell that can differentiate along Merkel cell or keratinocyte lines 1,6,7 . Analogous neuroendocrine carcinomas in other organs, including lung and the gastrointestinal tract, may be epithelial in origin as well 2…”

“…Merkel cell carcinoma and squamous lesions have similar risk factors, including solar radiation, transplantation, ectodermal dysplasia syndrome and arsenic, so it is possible that tumors with these two morphologies represent collision tumors 3 . However, this explanation for the link between the two does not account for the presence of transition cells exhibiting features typical of both Merkel cell carcinoma and squamous cells, while the epidermal stem cell theory makes transitional cells a natural part of pathogenesis 3,5–7 …”

“…Although squamous differentiation is most common, Merkel cell carcinomas have also been reported to have lymphoepithelioma‐like, melanocytic, glandular and neuroblastic differentiation 3,9 . In addition, four cases of Merkel cell carcinomas with sarcomatous differentiation have been documented 1,2,6,7 . In two of these, there was a CD68‐positive pseudosarcomatous component to the tumor identified as atypical fibroxanthoma‐like components 2,7 .…”

“…Usually, the epidermis and adnexal structures are spared 3 . However, squamous differentiation is noted occasionally, and overlying epidermal lesions, including squamous carcinoma in situ and invasive squamous cell carcinoma, have been reported 5–7 …”