Small cell lung cancer (SCLC) has historically been treated as a largely homogeneous disease, despite its aggressive course and rapid development of treatment resistance.
In a new Journal of Thoracic Oncology review, Case CCC's Associate Director of Clinical Research and Developmental Therapeutics Program member, Afshin Dowlati, MD, and his team examine growing evidence that a rare subset of SCLC retaining functional retinoblastoma (Rb) protein may represent a biologically and therapeutically distinct entity.
The study, Retinoblastoma-proficient small cell carcinoma: A Novel entity with therapeutic vulnerability?, indicates that RB1-proficient disease could have important implications for precision therapy, despite being estimated to represent only about 6% of SCLC.
Preclinical work suggests that tumors with functional Rb signaling may be vulnerable to CDK4/6 inhibition, and an early clinical study of abemaciclib produced immediate tumor regression in one of two index patients. Emerging evidence also links RB1 status to differences in chemotherapy response and the tumor immune environment, raising the possibility that Rb-proficient tumors could be more responsive to immune checkpoint inhibition—potentially in combination with CDK4/6 inhibitors.
A major challenge is identifying these tumors: RB1 mutation status alone does not reliably establish functional Rb proficiency. The authors argue that morphology, protein biomarkers, genomics and transcriptomics may ultimately need to be integrated to identify patients most likely to benefit.