Primary cutaneous keratinocytic primordial carcinoma with triple differentiations into basal cell carcinoma, sqaumous cell carcinoma, and porocarcinoma

The author herein reports a hitherto undescribed entity of cutaneous primordial carcinoma with triple differentiation into basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and porocarcinoma (PC) in a 66-year-old man. The patient was treated by tumor excision with wide margins. Pathologically, the margins were negative for tumor cells. The patient is now healthy 1 year after the excision. The tumor measured 3 cm × 2 cm × 2 cm and arose from the epidermis. The percentage of the occupying area was 60% in BCC, 20% in SCC, and 20% in PC. Histologically, BCC was characterized by basalioma cells, melanin pigmentation, peripheral palisading, and cleft formation, SCC by ample acidophilic cytoplasm, individual keratinization and cancer pearls, and PC by poroma cells and tubular structures containing cuticles. Cystic changes in BCC and SCC, keratotic nature of BCC, and acatholytic features of SCC were also seen in places. There were gradual merges among the three components. Immunohistochemically, BCC component was characterized by strong and diffuse expression of KIT, PDGFRA and p63, weak expressions of cytokeratin (CK) AE1/3, CK CAM5.2, CK34BE12, and negative expressions of CK18, CK19, CEA and CA19-9. SCC component was characterized by strongly positive expressions of p63, CEA, CK34BE12, CK7 and CK8, and negative expressions of CK18, CK19, and CA19-9. PC was characterized by strongly positive expressions of KIT, PDGFRA, CK34BE12, CK7, CK8, CK18, CK19, CEA, S100 protein, CA19-9, MUC1, and negative expression of p63. The present case revealed that there are primary cutaneous keratinocytic primordial carcinomas with triple differentiations into BCC, SCC, and PC. The present case is the first example of such tumors. It is thought that KIT and PDFRA-positive stem cells or cancer stem cells in the BCC component give rise to the SCC and PC components in the present case.