SAN FRANCISCO – The immune checkpoint inhibitor pembrolizumab (Keytruda) was associated in a small case series with remarkable overall and progression-free survival of patients with pulmonary sarcomatoid carcinoma (PSC), a rare variant of non–small cell lung cancer (NSCLC) with a grim prognosis.
Among five patients with PSC, three of whom were treatment naive, none experienced disease progression on pembrolizumab after a median follow-up of 13 months – although one died from a fungal infection unrelated to therapy – with the longest overall survival to date out to 33 months.
In contrast, patients with PSC treated before the advent of immunotherapy had a median progression-free survival of just 2 months and median overall survival a brief 4-6 months, reported, and his colleagues at the Albert Einstein College of Medicine, New York.
“It’s a uniquely enriched population of patients with lung cancer that have the best prognosis in terms of benefits from checkpoint inhibitors,” he said in an interview at the ASCO-SITC Clinical Immuno-Oncology Symposium.
PSC, a poorly differentiated subtype of NSCLC, accounts for about 0.3%-1.3% of all cases of lung cancer. It is closely associated with a history of heavy cigarette smoking and is rapidly fatal, with a poor response to conventional chemotherapy, although approximately 20% of patients with PSC have MET exon 14–skipping mutations that are “exquisitely” sensitive to crizotinib (Xalkori), Dr. Sukrithan explained.
PSC tumors are also unique in that they have extraordinarily high levels of programmed death-ligand 1 (PD-L1), the target of immune checkpoint inhibitors, with tumor proportion scores exceeding 90% in some cases.
Additionally, up to 43% of PSC tumors have been found to have a high mutational burden, with more than 10 mutations per megabase, suggesting that these tumors may be especially attractive targets for checkpoint inhibitor therapy, he said.
The investigators retrospectively studied surgical pathology and treatment records for all patients with advanced PSC diagnosed at their center from June 2015 to June 2018 who received pembrolizumab. They performed immunohistochemistry testing on tissue samples from the patients to quantify PD-L1 expression.
They compared the results with a cohort of patients with advanced PSC diagnosed from June 2012 to June 2015, prior to the clinical availability of anti-PD-1/PD-L1 checkpoint inhibitors.
The PD-L1-treated cohort included two men and three women, ranging from 48 to 67 years, with smoking pack-years ranging from 24 to 50. Two of the patients had received prior chemotherapy followed by pembrolizumab, and the remaining three received pembrolizumab monotherapy.
Tumor proportion scores ranged from more than 75% of tumor cells examined in one patient to 100% of cells in another.
The objective response rate to pembrolizumab was 80% consisting of one complete response and three partial responses. The fifth patient continued to have stable disease out to more than 17 months.
“This highly treatment-refractory disease now should be carefully assessed for immuno-oncologic and molecularly targeted options, which are associated with significant improvement in outcomes,” the investigators wrote in a poster presentation.
The study was internally funded. Dr. Sukrithan reported having no disclosures.
SOURCE: Sukrithan V et al. ASCO-SITC, .