Transformation from Small Cell to Squamous Cell Carcinoma in a Thymic Carcinoma Patient with a Durable Response to Anlotinib: A Case Report

The most common pathologic type of thymic carcinoma (TC) is squamous cell carcinoma (SCC). Small cell carcinoma is relatively rare, accounting for approximately 2% to 5% of all thymic tumors. Histologic transformation of TC has not yet been reported. Available treatments for TC patients who progress after first-line therapy are limited, which contributes to their poor prognosis. We reported an extraordinary case of a 66-year-old man who was diagnosed with thymic small cell carcinoma that transformed into SCC after third-line treatment. Surprisingly, the patient had a progression-free survival (PFS) of 25 months and an overall survival (OS) of 10 years on anlotinib as fourth-line therapy. The tolerance was well. Thus, anlotinib may be a safe and promising treatment for TC patients, especially those who undergo histologic transformation.