Incidence and timing of recurrence after adjuvant Palbociclib in completely resected retroperitoneal liposarcoma

Introduction Aggressive surgical resection is the cornerstone of treatment for retroperitoneal sarcomas (RPS), but recurrent disease occurs in up to 50% of patients. Palbociclib, an oral CDK4/6 inhibitor, in adjuvant setting may delay the need for additional surgery. However, it is unclear which patients derive an oncologic benefit from Palbociclib and what duration is required to prevent recurrence. We sought to evaluate recurrence patterns in patients with high risk RPS who completed adjuvant Palbociclib. Methods Patients with no evidence of disease after resection of RPS and treated with adjuvant Palbociclib were identified from a prospectively-maintained institutional database. We performed bulk RNA sequencing of primary tumor samples. Results Of the thirty-four patients who received adjuvant Palbociclib, 8 met the inclusion criteria and 5 developed recurrence after stopping treatment. Most (n=7) patients completed at least 12 months of Palbociclib. The three patients without recurrence currently have disease-free interval of 16, 25, and 33 months. On RNA sequencing, the epithelial-mesenchymal transition pathway is significantly enriched in the recurrence cohort compared to the no-recurrence cohort. Conclusion Half of the patients in this cohort developed short interval recurrence after completing adjuvant Palbociclib. Studies with larger patient cohorts and genomic analysis of tumors may lend additional insight.