Pilomatrix carcinoma with lymph node and pulmonary metastasis: report of a case arising on the knee

A 58-year-old woman presented with a pilomatrix carcinoma on the right knee. The tumor developed at the site of a previous lesion that had been present since she was 30 years old. Histologic study showed the presence of basaloid cells with numerous atypical mitoses, shadow cells, and calcification. After several surgical excisions, the tumor mass infiltrated the subcutaneous tissue, muscle, and bone, resulting in inguinal lymph node and pulmonary metastasis. We also review the literature and comment on the histopathologic differences from other cutaneous tumors.