Triple negative breast cancer (TNBC) a clinically aggressive subtype of breast cancer with poor outcomes. Chromosomal instability is a hallmark of many TNBCs, and likely underlies its ability to adapt and rapidly become resistant to chemotherapy. A study of residual disease after neoadjuvant chemotherapy have identified biological mechanisms driving this resistance to chemotherapy. Copy number amplifications such as MCL1, MYC and JAK2, as well as PTEN deletions or mutations have all been identified at a higher frequency in residual disease, suggesting they may play a role in de novo or acquired chemotherapy resistance. Increased copy number and expression of the PIM1 proto-oncogene in TNBC has also been identified as a new target of chemotherapy resistance. However, given the genomic instability and subclonal nature of driver mutations in TNBC, single agent targeted therapy is unlikely to be effective. Lately immune evasion has also been identified as another key characteristic of poor prognostic and chemo-resistant primary TNBCs. Combinations of checkpoint inhibition with targeted therapy and/or chemotherapy are currently being investigated.
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