Clinical sequencing defines the somatic and germline mutation landscapes of Chinese HER2-Low Breast Cancer.

More than half of the breast cancer initially labeled as human epidermal growth factor receptor 2 (HER2)-negative actually exhibited low HER2 levels (IHC 1+ or IHC 2+/FISH-) and were classified as HER2-low breast cancer. Previous research emphasized the significant biological heterogeneity in HER2-low breast cancer, highlighting the importance of accurately characterizing HER2-low tumors to promote the precise management of antibody‒drug conjugates. In this study, we established a large-scale targeted sequencing cohort (N = 1907) representing Chinese HER2-low breast cancer patients with detailed clinical annotation. Our research findings revealed that HER2-low breast cancer demonstrated distinct clinical pathological characteristics and mutation landscapes compared to HER2-zero group. When compared to HER2-zero tumors, HER2-low tumors exhibited a higher proportion of Luminal B subtypes and better disease-free survival. In hormone receptor (HR)-positive breast cancer, HER2-low group showed a higher frequency of GATA3 somatic mutations, BRCA2 germline mutations, and mutations in the DNA damage repair pathway. In contrast, in HR-negative breast cancer, the HER2-low group displayed a higher frequency of PIK3CA mutations and PI3K pathway alterations. These findings offered valuable insights for the precise targeted treatment of HER2-low breast cancer in different HR statuses.

Clinicopathological Characteristics and Survival Outcomes of Mammary Paget's Disease: A Retrospective Study Based on a Chinese Population.

BACKGROUND: Mammary Paget's disease (PD) is a rare type of breast cancer. Most cases of PD are presented with underlying ductal carcinoma in situ (DCIS) or invasive breast carcinoma (IDC). This study aimed to investigate the clinicopathological characteristics and survival outcomes of PD patients. MATERIALS AND METHODS: A total of 406 patients diagnosed with PD with IDC/DCIS at Fudan University Shanghai Cancer Center (FUSCC) were recruited as the PD group, 1218 patients diagnosed with IDC/DCIS alone during the same period were selected as the non-PD group, and the clinicopathological results of these two groups were compared. The Surveillance, Epidemiology, and End Results (SEER) database was used to investigate the clinicopathological features between PD and non-PD patients for validation. RESULTS: Compared with the non-PD group, the PD group was much more likely to have larger (≥2 cm: 43.1% vs 35.5%, P < 0.001), less hormone receptor (HR)-positive (68.5% vs 26.6%, P < 0.001), more human epidermal growth factor receptor-2 (HER-2)-positive (70.7% vs 27.5%, P < 0.001) and higher Ki-67 proportion (51.5% vs 42.5%, P < 0.001) tumors. The HER-2 overexpression subtype accounted for the largest proportion in the PD-IDC group and the lowest proportion in the non-PD-IDC group (54% vs 8%, P < 0.01). Moreover, the PD group had significantly worse disease-free survival (DFS) than the non-PD group (5-year DFS: 91.8% vs 97.3%, P = 0.001), and the SEER database showed a similar trend. Univariate and multivariate Cox regression analyses demonstrated that PD was an independent poor-risk factor. Our matched study showed that the PD group had worse survival than the non-PD group after excluding age, HR, HER-2, tumor size and lymph node status. CONCLUSION: PD with IDC/DCIS is associated with more aggressive tumor characteristics and worse survival outcomes. More than half of PD breast cancers are HER-2 overexpression subtype. PD is an independent poor-risk factor for breast cancer survival.

Large-scale genomic sequencing reveals adaptive opportunity of targeting mutated-PI3Kα in early and advanced HER2-positive breast cancer.

BACKGROUND: Few studies have discussed the contradictory roles of mutated-PI3Kα in HER2-positive (HER2+) breast cancer. Thus, we characterised the adaptive roles of PI3Kα mutations among HER2+ tumour progression. METHODS: We conducted prospective clinical sequencing of 1923 Chinese breast cancer patients and illustrated the clinical significance of PIK3CA mutations in locally advanced and advanced HER2+ cohort. A high-throughput PIK3CA mutations-barcoding screen was performed to reveal impactful mutation sites in tumour growth and drug responses. RESULTS: PIK3CA mutations acted as a protective factor in treatment-naïve patients; however, advanced/locally advanced patients harbouring mutated-PI3Kα exhibited a higher progressive disease rate (100% vs. 15%, p = .000053) and a lower objective response rate (81.7% vs. 95.4%, p = .0008) in response to trastuzumab-based therapy. Meanwhile, patients exhibiting anti-HER2 resistance had a relatively high variant allele fraction (VAF) of PIK3CA mutations; we defined the VAF > 12.23% as a predictor of poor anti-HER2 neoadjuvant treatment efficacy. Pooled mutations screen revealed that specific PI3Kα mutation alleles mediated own biological effects. PIK3CA functional mutations suppressed the growth of HER2+ cells, but conferred anti-HER2 resistance, which can be reversed by the PI3Kα-specific inhibitor BYL719. CONCLUSIONS: We proposed adaptive treatment strategies that the mutated PIK3CA and amplified ERBB2 should be concomitantly inhibited when exposing to continuous anti-HER2 therapy, while the combination of anti-HER2 and anti-PI3Kα treatment was not essential for anti-HER2 treatment-naïve patients. These findings improve the understanding of genomics-guided treatment in the different progressions of HER2+ breast cancer.