TP53-positive clones are responsible for drug-tolerant persister and recurrence of HER2-positive breast cancer.

PURPOSE: The prognosis of HER2-positive breast cancer has improved with the development of anti-HER2 therapies. In order to further improve the prognosis of HER2-positive breast cancer, it is essential to elucidate the cells that survive during the therapy (drug-tolerant persister DTP).

METHODS

Of the 2022 breast cancer patients operated at our institution during 2004-2018, 240 (12%) had HER2-positive breast cancer. Neo-adjuvant chemotherapy including trastuzumab (Tr-NAC) was administered to 94 of them. Forty-six of them were complete remission (CR), and 48 were non-CR. After 6.9 ± 3.7 years of follow-up, all 46 CR cases showed no recurrence (Cohort A), and 48 non-CR cases were divided into 31 cases with no recurrence (Cohort B) and 17 cases with recurrence (Cohort C). In addition to clinical backgrounds, we compared genomic profiles for 27 patients (Cohort A; 15/48, B; 7/31, and C; 5/17) who consented to genomic analysis.

RESULTS

Genomic abnormalities of TP53 and PIK3CA were frequently observed in biopsy samples pre Tr-NAC, but we found no differences between CR (Cohort A) and non-CR (Cohorts B + C). Then, we examined both of pre and post Tr-NAC samples of Cohort B (7) and C (5) to see the relationship between recurrence and genomic abnormalities. TP53 mutations were significantly more prevalent in Cohort C (5/5, 100%) than cohort B (3/7, 43%) in the surgical sample after treatment (p = 0.04). PyClone analysis of TP53 mutations showed that the cellular frequency of TP53 clones increased in 4 of 5 patients in Cohort C and none of B. On the other hand, we found no enhancement of PIK3CA mutant clones in Cohort C.

CONCLUSIONS

The DTP after Tr-NAC associated with subsequent relapse had TP53 mutations, suggesting that overcoming DTP with TP53 mutations is the most important clinical challenge.

TRIAL REGISTRATION: Not applicable.