breast-cancer

Study identifies how BRCA-mutant breast cancer builds resistance to PARP inhibitors—and how to overcome it.

Patient samples from a Phase II neoadjuvant talazoparib trial (NCT03499353) revealed two resistance mechanisms: (1) BRN2 overexpression activating ATR/RAD51 and STAT3 pathways to restore HR repair (reversible with ATR and STAT3 inhibitors); (2) pre-existing SHLD2-deficient tumor subclone expansion.…

Dan Manning

Dan Manning

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Study identifies how BRCA-mutant breast cancer builds resistance to PARP inhibitors—and how to overcome it.

Study identifies how BRCA-mutant breast cancer builds resistance to PARP inhibitors—and how to overcome it.

Patient samples from a Phase II neoadjuvant talazoparib trial (NCT03499353) revealed two resistance mechanisms: (1) BRN2 overexpression activating ATR/RAD51 and STAT3 pathways to restore HR repair (reversible with ATR and STAT3 inhibitors); (2) pre-existing SHLD2-deficient tumor subclone expansion. PDX models confirmed both mechanisms in vivo.

Key Findings

  • BRN2 overexpression restores HR repair via ATR/RAD51 and STAT3 pathways—conferring acquired PARPi resistance
  • ATR and STAT3 inhibitors reversed BRN2-driven resistance
  • SHLD2-deficient tumor subclone expansion represents intrinsic resistance
  • Both acquired and intrinsic mechanisms identified from a clinical trial
  • PDX models confirmed resistance patterns in vivo

Implications

Pre-treatment profiling for BRN2 and SHLD2 status could identify patients likely to resist neoadjuvant PARPi. Combination with ATR and/or STAT3 inhibitors may overcome acquired resistance.

Caveats

Based on small Phase II trial; abstract-only. PDX models are limited representations. Neoadjuvant-specific mechanisms may differ from adjuvant settings.

Source: Proceedings of the National Academy of Sciences of the United States of America — 2026-04-21

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