Preliminary safety and activity results of trabectedin in a phase II trial dedicated to triple-negative (ER-, PR-, HER2-), HER2+++, or BRCA1/2 germ-line-mutated metastatic breast cancer (MBC) patients (pts)

Abstract

1010 Background: Trabectedin ([T]; Yondelis) binds to the minor groove of DNA; its cytotoxicity is determined by the synergistic action of two DNA repair mechanisms, the efficient nucleotide excision repair (NER) and deficient homologous recombination repair (HRR) machinery. T has EMEA authorization in soft tissue sarcoma after failure of standard treatment. Preliminary data have shown activity of T as single agent in MBC. Clinical and preclinical data suggested T may display specific activity among certain NER-intact or HRR-deficient MBC, and prompted this phase II trial dedicated to 3 subgroups: triple-negative (TN), HER-2-overexpressed, and BRCA1/2 germline-mutated MBC. Methods: T was given at 1.3 mg/m2 as a 3- hour iv infusion every 3 weeks to pts with pretreated progressive MBC: Group A: TN; Group B: HER-2+++; Group C: BRCA1/2 mutation carriers. Endpoints were objective response (OR) rate by RECIST, duration of response, progression free survival (PFS), tumor volume changes, safety and exploratory pharmacogenomics (PGx). Results: A total of 95 women (median [med] age 52, ECOG 0/1 48/52%) have been enrolled (A:50, B:24, C:21) with data available for 72 pts. Med number of prior chemotherapy regimens: 4 (1–10). Med number of T cycles administered: 2 (1–12) for all groups. The most commonly reported grade 3/4 AEs are neutropenia (29/21%), ALT (28/2%) and AST (13/0). Alopecia/stomatitis, only G1, was reported in <2% each. Long-lasting disease stabilizations were described in all groups. While OR were rare among TN MBC pts (2PR/43 evaluable), preliminary analysis by investigator shows efficacy in group C (4PR/11 evaluable). Tissue samples from 36 pts were collected for RNA expression analysis (XPG + ERCC1 + BRCA1). Preliminary results show high XPG is associated with longer PFS: 4.1 months (95% CI 2.6-not reached) versus 1.3 months (95% CI 1.2–3.7), p = 0.01. Analyses are ongoing. Conclusions: Trabectedin shows a manageable safety profile in the 3 groups of MBC with promising efficacy in certain DNA-repair machinery sub-categories defined molecularly. TN group was closed due to low response. More mature PGx results will be discussed to help selecting the patients who are at highest chance for response. [Table: see text]