Outcome of EGFR-mutated adenocarcinoma NSCLC patients with changed phenotype to squamous cell carcinoma after tyrosine kinase inhibitors: A pooled analysis with an additional case.

The onset of a new histology is a resistant mechanism to tyrosine kinase inhibitors (TKI) in lung adenocarcinoma (ADK), but this phenomenon has not yet been fully clarified. We present a pooled analysis of the outcomes of EGFR-mutated ADK patients with changed phenotype to squamous cell carcinoma (SqCC) following TKI, along with the description of an additional case. A 67-year-old woman with EGFR-mutated NSCLC received gefitinib and subsequently osimertinib, due to the presence of T790 M at progression. The re-biopsy after third-generation TKI revealed SqCC histology along with the basal EGFR mutation, while T790 M disappeared. The patient rapidly progressed and died despite two chemotherapy cycles. Since this first description of SqCC transformation appearing after treatment with the third-generation TKI osimertinib, other 16 patients, with EGFR-mutated ADK developing a transformation to SqCC histology after treatment with TKIs, were up to now published. From our pooled analysis emerged that most patients were female (82%), 41% were former smokers and no current smokers were identified. Median time to SqCC onset was 11.5 months. In all cases, basal EGFR mutation was maintained, and 11 patients (65%) developed an acquired mutation on exon 20. Interestingly also 790 M mutation appeared in 8 patients (47%). The median survival after SqCC diagnosis was 3.5 months regardless the treatments received. Therefore, EGFR-mutated lung ADK destined to develop a squamous phenotype were often smokers and maintained the baseline genomic alterations. The prognosis after SqCC diagnosis was extremely poor and current treatments largely inefficacious.