A look towards the clonal origin of metastatic pulmonary carcinosarcoma: Report of a patient with an unexpected long-term survival.

INTRODUCTION: Pulmonary carcinosarcoma is a rare histological subtype of non-small cell lung cancer, defined by the combination of epithelial and mesenchimal elements. Prognosis is usually dismal, with a median survival of about 6 months. The use of immunotherapy by blockade of PD1/PD-L1 immune checkpoint signaling has been shown to improve patients' survival. However, local aggressiveness and distant metastases are frequent. Spread to the gastrointestinal tract is seldom reported. The genetic landscape of the disease has only recently begun to emerge, pointing at TP53, KRAS, EGFR and MET as the most common mutated genes. CASE DESCRIPTION: We describe the case of a metastatic patient with 37 months overall survival, treated by an aggressive multimodal approach combining surgery, chemotherapy, radiotherapy and immunotherapy. To shed new light on the molecular basis for sarcomatoid component in lung carcinoma, we performed next generation sequencing analysis of the squamous and sarcomatoid component by the two sites. We demonstrated a clonal origin and hypermutability of the sarcomatous elements that may account for the good response to immunotherapy. Moreover, we identified some mutations involving TP53 and EGFR genes, targetable by already available drugs. CONCLUSIONS: We depicted a model of how a squamous cell carcinoma can differentiate during its natural history into sub-clonal populations with different features and may ultimately result in a neoplasm (i.e. pulmonary carcinosarcoma) showing clonal heterogeneity. Our data might contribute to a better understanding of the pathogenesis and molecular mechanisms of this rare tumor and open new ways for a more tailored approach.