Unraveling complexity and leveraging opportunities in uncommon breast cancer subtypes.

Special histologic subtypes of breast cancer (BC) exhibit unique phenotypes and molecular profiles with diagnostic and therapeutic implications, often differing in behavior and clinical trajectory from common BC forms. Novel methodologies, such as artificial intelligence may improve classification. Genetic predisposition plays roles in a subset of cases.

Incidence of Adjacent Synchronous Ipsilateral Infiltrating Carcinoma and/or Ductal Carcinoma In Situ in Patients Diagnosed with Flat Epithelial Atypia by Core Needle Biopsy (TBCRC 034).

Background: Flat epithelial atypia (FEA), a rare breast proliferative lesion, is often diagnosed following core biopsy (CB) of mammographic microcalcifications. In the prospective multi-institution TBCRC 034 trial, we investigate the upgrade rate to ductal carcinoma in situ (DCIS) or invasive cancer following excision for patients diagnosed with FEA on CB.

Patients And Methods: Patients with a breast imaging reporting and data system (BI-RADS) ≤ 4 imaging abnormality and a concordant CB diagnosis of FEA were identified for excision.

Active Monitoring With or Without Endocrine Therapy for Low-Risk Ductal Carcinoma In Situ: The COMET Randomized Clinical Trial.

Importance: Active monitoring for low-risk ductal carcinoma in situ (DCIS) of the breast has been proposed as an alternative to guideline-concordant care, but the safety of this approach is unknown.

Objective: To compare rates of invasive cancer in patients with low-risk DCIS receiving active monitoring vs guideline-concordant care.

Design, Setting, And Participants: Prospective, randomized noninferiority trial enrolling 995 women aged 40 years or older with a new diagnosis of hormone receptor-positive grade 1 or grade 2 DCIS without invasive cancer at 100 US Alliance Cancer Cooperative Group clinical trial sites from 2017 to 2023.

Serous-like breast carcinomas: immunophenotypic, genetic, and clinicopathologic characterization of a morphologically distinct group of tumours.

Aims: Unusual morphologic patterns of breast carcinomas can raise diagnostic consideration for metastasis or special breast cancer subtypes with management implications. We describe rare invasive breast cancers that mimic serous carcinoma of the gynaecologic tract (serous-like breast carcinomas, SLBC) and characterize their clinicopathologic, immunophenotypic, and genetic features.

Methods And Results: All patients were female (n = 15, median age 49 years) without a history of gynaecologic malignancy.