Transformation or Clonal Evolution? A Rare Case Report of Pulmonary Sarcomatoid Carcinoma Developing to Small Cell Lung Cancer

Many cases of non-small cell lung cancer (NSCLC) transforming to small cell lung cancer (SCLC) after targeted therapy have been reported, most of which are associated with acquired resistance mutations. Herein, we report the first documented case of phenotypic conversion to SCLC in a patient with advanced pulmonary sarcomatoid carcinoma (PSC) who received pemetrexed, carboplatin, and camrelizumab only, with no targeted agents administered. Through comparative analysis of two serial pathological biopsies and genetic profiling, our findings suggest that PSC may undergo clonal evolution or alternative transformation mechanisms under therapeutic pressure. TP53 and RET mutations may be implicated in this phenotypic transition. This case provides new insights into the biological mechanism underlying the evolution of PSC to SCLC.