Epidermal growth factor receptor mutation heterogeneity analysis of pulmonary sarcomatoid carcinoma successfully treated with erlotinib: A case report.

Pulmonary sarcomatoid carcinoma (PSC) is a rare histological subtype of non-small cell lung cancer, and the available studies on the response to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) is limited. In the present study, a 73-year-old female presented with a large mass in the lower right lung, which was diagnosed as a PSC on biopsy. An amplification-refractory mutation system (ARMS) test revealed that the patient possessed the wild-type EGFR gene, and the patient subsequently underwent radiotherapy (60 Gy) and four 21-day cycles of chemoradiotherapy (1,600 mg gemcitabine, days 1 and 8; 30 mg, cisplatin, days 1-3). Following radiotherapy and chemotherapy treatment, a CT scan revealed complete remission of the mass in the lower right lung, however, metastases were identified in the paraaortic lymph node, bilateral iliac fossa and the right gluteal region. Notably, an EGFR exon 21 L858R gene mutation was identified in the mass of the right gluteal metastasis. Therefore, treatment with erlotinib was initiated. The patient continued to experience progression-free survival for six months following the initiation of erlotinib therapy. However, multiple metastases were then identified, and all lesions possessed the wild-type EGFR gene, as identified by the ARMS test. The findings suggest that erlotinib is a viable therapeutic option for the treatment of PSC patients that possess an EGFR mutation. The spatio-temporal evolution of EGFR mutational heterogeneity in PSC may result in drug-resistance, which challenges EGFR-TKI therapy and EGFR gene mutation diagnosis.