LAUSR

Tumor-to-tumor metastasis is a very rare finding that was first reported in 1902. The criteria applied by Campbell et al in their 1968 review of previously published cases have since gained widespread acceptance in defining true tumor-to-tumor metastases: (1) evidence of 2 or more primary tumors with the recipient tumor being a true neoplasm, (2) exclusion of tumor emboli or direct invasion from an adjacent tumor, and (3) exclusion of metastatic tumors that involve lymph nodes already involved by lymphoproliferative diseases. As with all other forms of tumor-to-tumor metastases, melanoma metastasizing to other neoplasms is a rare finding. We report herein a case of a 62-year-old male who was recently diagnosed with melanoma metastatic to basal cell carcinoma of skin. The patient underwent a wide local excision for an invasive melanoma of the right flank skin (clinical stage III, pT4b) and subsequently developed widely metastatic systemic disease. During a routine follow-up clinic visit, he was found to have several cutaneous lesions, including a 2-cm raised lesion on the parietal scalp that was ultimately biopsied. This lesion showed aggregates of melanoma cells that appeared to have metastasized to a preexisting basal cell carcinoma of the nodular/ nodulocystic subtype (Figure 1A and B). There was no intraepidermal component, although the basal cell carcinoma component showed areas of surface ulceration. Immunohistochemical studies for MART-1 differentially highlighted the metastatic melanoma (Figure 1C), whereas Ber-EP4 highlighted the basal cell carcinoma (Figure 1D). A rare example of tumor-to-tumor metastasis is reported herein, in the form of melanoma metastatic to a basal cell carcinoma of skin. This rare occurrence has been previously reported and should be distinguished from the so-called 668032 IJSXXX10.1177/1066896916668032International Journal of Surgical PathologyLowenthal and Fadare research-article2016