Retinoblastoma Proficient Small Cell Carcinoma: A Novel Entity with Therapeutic Vulnerability?

Small-cell lung cancer (SCLC), frequently characterized by early metastasis and rapid development of therapy resistance, remains the most aggressive form of lung cancer. Recent transcriptional profiling has redefined SCLC as a heterogeneous spectrum of biologically distinct subtypes with potential differential therapeutic vulnerabilities, fostering optimism that molecular stratification may improve clinical outcomes. Within this framework, growing interest has focused on the rare subset of SCLC that retains functional retinoblastoma (Rb) protein. While recognizing Rb-proficient SCLC as a distinct entity continues to evolve, transcriptomic correlations suggest possible links with YAP1 and non-neuroendocrine expression programs. Preclinical studies further indicate that Rb protein retention may confer unique therapeutic sensitivity, particularly to CDK4/6 inhibition, which not only suppresses tumor proliferation but also potentially reshapes the immune microenvironment to enhance immunotherapy responses. More importantly, RB1 functional status may also modulate sensitivity to additional therapeutic modalities, highlighting its broader relevance to the evolving SCLC treatment landscape. Integrating molecularly informed strategies accounting for RB1 proficiency and its transcriptional landscape will be pivotal to overcoming the long-standing therapeutic impasse in SCLC, offering a roadmap for the development of effective, precision-guided therapies.