Durable response to palbociclib and letrozole in ovarian cancer with loss.

Alterations of the Retinoblastoma (Rb) pathway are frequent in ovarian cancer, typically resulting from down-regulation, amplification, amplification, and loss. However, bi-allelic mutation or homozygous deletion is a very rare event, concerning less than 5% of patients.Initial trials with palbociclib in serous ovarian cancer have shown very modest benefit in unselected patient populations, thus underlining the need for a biomarker predicting response. We report the case of a heavily pre-treated patient with a serous ovarian tumor harboring a homozygous deletion of the gene that derived significant, prolonged clinical benefit from palbociclib, a CDK4/6 oral inhibitor, with letrozole. Treatment with palbociclib and letrozole started on February 2018, with an ongoing response after 12 months.In conclusion, homozygous deletion is rare and could be used to predict response to CDK4/6 inhibitors in association with other genomic features. We encourage further trials in this direction.