Negative/Low Hormone Receptor And/or HER2 POsitive Lobular Invasive Breast Carcinoma - A Real-World International Cohort Study

The NAPOLI Study is a retrospective multicenter observational study designed to characterize hormone receptor-negative/low invasive lobular carcinoma of the breast. The study will collect real-world clinicopathological, molecular, therapeutic and outcome data from patients diagnosed and treated at participating centers. The aim is to describe the clinical behavior, pathological features, receptor profile, treatments received and oncologic outcomes of this rare breast cancer subtype.

Inclusion Criteria: * Female or male patients aged ≥18 years; * Histologically confirmed ILC, confirmed by E-cadherin loss/aberrant expression and/or p120 cytoplasmic relocalization and/or CDH1 alteration; * HR-negative (ER \50% lobular) and HR-negative/low criteria are met; * Stage I-III disease at diagnosis; Patients with de novo stage IV disease who underwent surgery of the primary tumor will not be included in the main study cohort but may be captured in a separate exploratory cohort for dedicated analysis; * Patients who underwent surgery of the primary tumor at the participating institution, either upfront or after neoadjuvant systemic treatment; * Diagnosis occurred between 1 January 2000 and 31 December 2025; * Minimum follow-up of 12 months for patients without an event, unless recurrence or death occurred earlier; * Local review by a dedicated breast pathologist to confirm the diagnosis and the related molecular features, with particular attention to the confirmation of apocrine morphology. Exclusion Criteria: * Pure IC NST without any lobular invasive component; * ER or PR expression \>10% in the invasive component, in cases with negative HER2 status; * In situ lobular neoplasia (lobular carcinoma in situ) without an invasive component; * De novo stage IV disease (such patients, if they underwent surgery of the primary tumor, will be captured in a separate exploratory cohort for a dedicated analysis) * Synchronous invasive BC of another dominant histology requiring systemic treatment that precludes attribution of outcomes to HR-negative/low ILC; * Prior invasive BC under active systemic treatment at the time of diagnosis, unless clearly documented as unrelated and not expected to confound outcomes; * Insufficient data or follow up