Primary cutaneous
small cell carcinoma (PC-SmCC) is extremely rare; only two cases have been reported in the world literatures. A 79-year-old woman presented a small cutaneous
tumor in the face. Physical examination showed a
tumor measuring 1.0x.08x0.6 cm in the shallow skin of the face. Excisional skin biopsy was performed. The biopsy showed complete excision of the
tumor. The
tumor was located in the shallow dermis and no connections to epidermis were seen. The
tumor was invasive into subcutaneous tissue and surrounding dermis. The
tumor was very hypercellular
tumor composed of small cells with scant cytoplasm, hyperchromatic nu lei, negative nucleoli, and molded nuclei. The shapes of
tumor cells are round, ovoid or spindle. The histological appearances fulfilled the criteria of SmCC of WHO. Immunohistochemically, the
tumor cells were positive for
cytokeratin (CK) AE1/3, CK
CAM5.2, CK34BE12, CD5, CD6, CK8, p63, NSE,
NCAM,
synaptophysin (focal),
chromogranin (focal), p53, KIT, PDGFRA and Ki-67 (labeling index (LI)=86%). They were negative for CK7, CK19, CK20, EMA,
vimentin, CEA,
S100 protein, CA19-9, TTF-1, MUC1, MUC2, MUC5AC and MUC6.
Mucin histochemistry revealed no
mucins. A molecular genetic analysis of PCR-direct sequencing identified no mutations of KIT (exons 9, 11, 13, and 17) and PDGFRA (exons 12 and 18) genes. The author diagnosed this cutaneous
tumor as SmCC. Post-diagnosis whole body examination using various imaging and endoscopic techniques revealed no
tumors. This may confirm that the skin
tumor was primary. The cutaneous
tumor was completely resected with wide margins. The patient is now followed up without
therapy 8 months after the diagnosis. No recurrence or
metastasis is seen. The differential diagnosis from
Merkel cell carcinoma and
basal cell carcinoma is very difficult and herein discussed.