Solitary Lymphatic Metastatic Lesion From Dorsal Hand Cutaneous Squamous Cell Carcinoma: A Diagnostic Dilemma Between In-Transit and Interval Nodal Metastasis.

Lymphatic metastatic lesions arising between a primary cutaneous squamous cell carcinoma (cSCC) and the regional nodal basin present a diagnostic dilemma between in-transit metastasis (ITM) and interval nodal metastasis. We report the case of an immunocompetent octogenarian woman with a well-differentiated cSCC on the dorsum of the hand that was excised with clear margins. Six months later, a solitary subcutaneous nodule developed along the ipsilateral upper arm. Magnetic resonance imaging suggested a benign soft-tissue tumor, and an excisional biopsy was performed. Histopathological examination revealed a moderately differentiated squamous cell carcinoma morphologically similar to the primary lesion, located within a lymph node-like structure containing residual lymphoid architecture. Positron emission tomography-computed tomography showed no additional nodal or distant metastases. Based on the anatomical location along the lymphatic drainage pathway and clinicopathological findings, the lesion was considered a lymphatic metastatic deposit with features overlapping ITM and interval nodal metastasis. The patient received adjuvant radiotherapy and remains disease-free at six months of follow-up. This case highlights the diagnostic challenge in distinguishing ITM from interval nodal metastasis in cSCC and underscores the importance of careful clinicopathological correlation when evaluating solitary subcutaneous lesions arising along lymphatic drainage pathways.