Background: We aimed to determine the distribution of intrinsic subtypes within HER2-low breast cancer (BC), and to describe the prognostic impact of HER2-low status on survival outcomes. Methods: This is a retrospective, observational study of primary BC extracted from The Cancer Genome Atlas dataset. We described the distribution of PAM50 intrinsic subtypes within HER2-low BC subtype according to hormonal receptor status (positive (HR+) and negative (HR−)). Secondly, we assessed the impact of HER2-low on survival outcomes (progression-free interval (PFI), disease-free interval (DFI), and overall survival (OS)). Results: We analyzed 804 primary BCs, including 410 (51%) HER2-low BCs (336 HR+ and 74 HR−). The proportion of HER2-enriched tumors was higher in the HER2-low/HR− group compared to HER2-low/HR+ (13.7% versus 1.2%, respectively). HER2-enriched tumors were more frequent in HER2-low/HR− and HER2-low/HR+ subtypes, compared to HER2-negative/HR− and HER2-negative/HR+ subtypes, respectively (13.7% versus 1.6% and 1.2% versus 0.5%, respectively). We observed no significant differences in PFI, DFI, and OS between HER2-low subtypes and each non-HER2-low subtype paired by HR status. Conclusions: Our characterization of PAM50 intrinsic subtypes within HER2-low breast cancer may explain the different clinical behaviors and responses to treatment, and ultimately support further investigation of new treatment strategies in the HER2-low category. Moreover, it highlights the importance of considering HR status in the HER2-low category.

Since human epidermal growth factor receptor-2 (HER2) characterization, going through clinical research and regulatory approval of HER2-targeted therapies, much has elapsed and is still unfolding. Hitherto, only breast cancer (BC) patients with HER2 immunohistochemistry 3+ or with HER2 gene fluorescence in-situ hybridization (FISH) amplification (a.k.a., HER2-positive BC) have benefited from anti-HER2 agents. In recent years, however, much of the research effort has been expanded, with positive outcomes being reached for formerly known HER2-negative BC that yet express HER2 to some degree (HER2 immunohistochemistry 1+ or 2+, but FISH negative) and are currently being classified as HER2-low BC for the purpose of trial enrollment. In this sense, our aim is to review the body of evidence of HER2-low BC that led to the study of first-generation anti-HER2 agents, like trastuzumab, and how they have failed to achieve any clinical applicability in this setting. In addition, we review new data that is leading to the growing success of the new generation of drugs, especially the promising HER2-directed antibody–drug conjugates. A narrative review is also performed regarding the rationale behind the consolidated and ongoing clinical trials studying anti-HER2 agents in combination with unrelated agents, such as immunotherapy, endocrine therapy, and CDK4/6 inhibitors. Hopefully, all this ongoing research effort will be able to extend the survival benefits seen with anti-HER2 agents in HER2-positive disease, at least to some degree, to the greater proportion of patients with HER2-low BC.

Triple negative breast cancer (TNBC) is an area of high unmet medical need in terms of new effective treatment strategies. Although breast cancer is traditionally considered a ‘cold’ tumor type, TN...

The incorporation of circulating tumor DNA (ctDNA) into the management of operable breast cancer (BC) has been hampered by the heterogeneous results from different studies. We aimed to assess the prognostic value of ctDNA in patients with operable (non metastatic) BC. A systematic search of databases (PubMed/Medline, Embase, and CENTRAL) and conference proceedings was conducted to identify studies reporting the association of ctDNA detection with disease-free survival (DFS) and overall survival (OS) in patients with stage I-III BC. Log-hazard ratios (HRs) were pooled at each timepoint of ctDNA assessment (baseline, after neoadjuvant therapy, and follow-up). ctDNA assays were classified as primary tumor-informed and non tumor-informed. Of the 3174 records identified, 57 studies including 5779 patients were eligible. In univariate analyses, ctDNA detection was associated with worse DFS at baseline [HR 2.98, 95% confidence interval (CI) 1.92-4.63], after neoadjuvant therapy (HR 7.69, 95% CI 4.83-12.24), and during follow-up (HR 14.04, 95% CI 7.55-26.11). Similarly, ctDNA detection at all timepoints was associated with worse OS (at baseline: HR 2.76, 95% CI 1.60-4.77; after neoadjuvant therapy: HR 2.72, 95% CI 1.44-5.14; and during follow-up: HR 9.19, 95% CI 3.26-25.90). Similar DFS and OS results were observed in multivariate analyses. Pooled HRs were numerically higher when ctDNA was detected at the end of neoadjuvant therapy or during follow-up and for primary tumor-informed assays. ctDNA detection sensitivity and specificity for BC recurrence ranged from 0.31 to 1.0 and 0.7 to 1.0, respectively. The mean lead time from ctDNA detection to overt recurrence was 10.81 months (range 0-58.9 months). ctDNA detection was associated with worse DFS and OS in patients with operable BC, particularly when detected after treatment and using primary tumor-informed assays. ctDNA detection has a high specificity for anticipating BC relapse.

PURPOSE: Detection of circulating tumor DNA (ctDNA) after neoadjuvant chemotherapy in patients with early-stage breast cancer may allow for early detection of relapse. In this study, we analyzed ctDNA using a personalized, tumor-informed multiplex polymerase chain reaction–based next-generation sequencing assay. METHODS: Plasma samples (n = 157) from 44 patients were collected before neoadjuvant therapy (baseline), after neoadjuvant therapy and before surgery (presurgery), and serially postsurgery including a last follow-up sample. The primary end point was event-free survival (EFS) analyzed using Cox regression models. RESULTS: Thirty-eight (86%), 41 (93%), and 38 (86%) patients had baseline, presurgical, and last follow-up samples, respectively. Twenty patients had hormone receptor–positive/human epidermal growth factor receptor 2–negative, 13 had triple-negative breast cancer, and 11 had human epidermal growth factor receptor 2–positive disease. Baseline ctDNA detection was observed in 22/38 (58%) patients and was significantly associated with Ki67 > 20% ( P = .036) and MYC copy-number gain ( P = .0025, false discovery rate = 0.036). ctDNA detection at presurgery and at last follow-up was observed in 2/41 (5%) and 2/38 (5%) patients, respectively. Eight relapses (seven distant and one local) were noted (median follow-up 3.03 years [range, 0.39-5.85 years]). After adjusting for pathologic complete response (pCR), ctDNA detection at presurgery and at last follow-up was associated with shorter EFS (hazard ratio [HR], 53; 95% CI, 4.5 to 624; P < .01, and HR, 31; 95% CI, 2.7 to 352; P < .01, respectively). Association between baseline detection and EFS was not observed (HR, 1.4; 95% CI, 0.3 to 5.9; P = .67). CONCLUSION: The presence of ctDNA after neoadjuvant chemotherapy is associated with relapse in early-stage breast cancer, supporting interventional trials for testing the clinical utility of ctDNA monitoring in this setting.