Small lymphocytic lymphoma obscuring microscopic tonsillar squamous cell carcinoma: an unknown occurrence with a known primary.

Head and neck squamous cell carcinoma (HNSCC) often presents with cervical lymph node metastases and at times the primary tumor cannot be identified despite extensive workup. Lymphoma is the second most common neoplasm in the head and neck region but is seldom synchronous with HNSCC and rarely involves regional mucosal sites. We report herein a rare occurrence of tonsillar involvement by small lymphocytic lymphoma (SLL) incidentally detected during the workup for a cervical lymph node SCC metastasis of a 52-year-old non-smoker male. The microscopic human papillomavirus-positive SCC involving the tonsillar surface and crypts was obscured by SLL leading to the initial designation of 'unknown primary'. The occult HNSCC are likely explained by small tumor size, quality and quantity of sampling, thoroughness of endoscopic, radiological and pathological assessment or a combination of the above. The coexistence of another tumor such as lymphoma has not yet been reported as a confounding factor in the workup for cervical SCC metastasis. Since oropharyngeal SCC can be very small and Waldeyer's ring is a common site for lymphoma involvement, identification of such rare collision tumors requires pathologists' awareness, extensive sampling and occasionally ancillary studies for the accurate diagnosis and staging essential for the correct management.