Metastatic Syringocystadenocarcinoma Papilliferum Mimicking Cutaneous Squamous Cell Carcinoma of Unknown Primary in a Young Patient.

We report an unusual case of metastatic syringocystadenocarcinoma papilliferum in an 18-year-old man who presented with cervical lymph node metastasis initially diagnosed as dedifferentiated squamous cell carcinoma of unknown primary. Extensive diagnostic workup failed to identify a primary tumor, until reexcision of a childhood scalp lesion revealed a deeply infiltrative adnexal neoplasm with ductal differentiation consistent with syringocystadenocarcinoma papilliferum, and comparison of the lymph node specimens with the scalp specimen showed cytological similarities. This case emphasizes that the working diagnosis should be questioned by the pathologist and the clinician when clinical characteristics do not seem to fit. It furthermore highlights the importance of the inclusion of prior pathology specimens into the pathological workup, and careful evaluation for ductal differentiation in atypical squamous cell carcinoma presentations.