HER2-Low Luminal Breast Carcinoma Is Not a Homogenous Clinicopathological and Molecular Entity.

BACKGROUND: With the development of some new antibody-drug conjugates, the HER2 classification of breast carcinomas now includes the HER2-low (H2L) category: IHC 1+, 2+ non-amplified by ISH, and double-equivocal carcinomas, mostly luminal, expressing hormone receptors (HR+). METHODS: We analyzed mutational status and transcriptomic activities of three HER2 effector pathways: PI3K-AKT, MAPK, and JAK-STAT, in association with clinicopathologic features, in 62 H2L carcinomas compared to 43 HER2-positive and 20 HER2-negative carcinomas, all HR+. RESULTS: H2L carcinomas had significantly lower histoprognostic grades and mitotic and Ki67 proliferation indexes than HER2-positive carcinomas. Their PIK3CA mutation rates were close to those of HER2-negative and significantly higher than in HER2-positive carcinomas, contrary to TP53 mutations. At the transcriptomic level, we identified three distinct groups which did not reflect the new HER2 classification. H2L and HER2-negative carcinomas shared most of clinicopathological and molecular characteristics, except HER2 membrane expression (mRNA levels). The presence of a mutation in a signaling pathway had a strong pathway activation effect. PIK3CA mutations were more prevalent in H2L carcinomas, leading to a strong activation of the PI3K-AKT signaling pathway even in the absence of HER2 overexpression/amplification. CONCLUSION: PIK3CA mutations may explain the failure of conventional anti-HER2 treatments, suggesting that new antibody-drug conjugates may be more effective.

Prognostic stratification ability of the CPS+EG scoring system in HER2-low and HER2-zero early breast cancer treated with neoadjuvant chemotherapy.

BACKGROUND: The CPS+EG scoring system was initially described in unselected early breast cancer (eBC) patients treated with neoadjuvant chemotherapy (NAC), leading to refined prognostic stratification, and thus helping to select patients for additional post-NAC treatments. It remains unknown whether the performance is the same in new biological breast cancer entities such as the HER2-low subtype. PATIENTS AND METHODS: Outcomes (disease-free (DFS) and overall survival OS)) of 608 patients with HER2-non amplified eBC and treated with NAC were retrospectively analyzed according to CPS-EG score. We compared the prognostic stratification abilities of the CPS+EG in HER2-low and HER2-0 eBC, analyzing ER+ and ER- tumors separately. RESULTS: In ER+ eBC, the CPS+EG scoring system seems to retain a prognostic value, both in HER2-low and HER2-0 tumors, by distinguishing populations with significantly different outcomes (good: score 0-1, poor: score 2-3, and very poor: score 4-5). Using C-indices for DFS and OS, CPS+EG provided the highest prognostic information in ER+ eBC, especially in HER2-0 tumors. In contrast, in ER- eBC, the CPS+EG does not appear to be able to distinguish different outcome groups, either in HER2-low or HER2-0 tumors. In ER- eBC, C-indices for DFS and OS were highest for pathological stage, reflecting the predominant prognostic importance of residual disease in this subtype. CONCLUSIONS: HER2-low status does not influence the prognostic performance of the CPS+EG score. Our results confirm the usefulness of the CPS+EG score in stratifying the prognosis of ER+ eBC after NAC, for both HER2-0 and HER2-low tumors. For ER- eBC, HER2-low status does not influence the performance of the CPS+EG score, which was lower than that of the pathological stage alone.

Case report: Immune response characterization of a pseudoprogression in a PD-L1-negative, TMB-low, KEAP1/STK11 co-mutated metastatic NSCLC.

A patient with a PD-L1-negative, TMB-low, KEAP1/STK11 co-mutated metastatic non-small cell lung cancer (NSCLC) experienced a multisite radiological progression at 3 months after initiation of chemoimmunotherapy as first-line treatment for metastatic disease. After the radiological progression, while she was not undergoing treatment, the patient had spontaneous lesions shrinkage and further achieved a prolonged complete response. Genomic and transcriptomic data collected at baseline and at the time of pseudoprogression allowed us to biologically characterize this rare response pattern. We observed the presence of a tumor-specific T-cell response against tumor-specific neoantigens (TNAs). Endogenous retroviruses (ERVs) expression following chemoimmunotherapy was also observed, concurrent with biological features of an anti-viral-like innate immune response with type I IFN signaling and production of CXCR3-associated chemokines. This is the first biological characterization of a NSCLC pseudoprogression under chemoimmunotherapy followed by a prolonged complete response in a PD-L1-negative, TMB-low, KEAP1/STK11 co-mutated NSCLC. These clinical and biological data underline that even patients with multiple factors of resistance to immune checkpoint inhibitors could trigger a tumor-specific immune response to tumor neoantigen, leading to complete eradication of the tumor and probably a vaccinal immune response.