Long‐term outcome of high‐grade encapsulated papillary carcinoma of the breast: implications for staging and management

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Abstract
Background: Encapsulated papillary carcinoma (EPC) of the breast is an uncommon tumour with controversial biological behaviour and staging. Emerging evidence suggests that EPC with adverse pathological features (EPC‐A) may exhibit invasive potential. The absence of uniform staging criteria contributes to management variability. This study evaluates the clinicopathological characteristics and clinical course of high‐grade EPC (HG‐EPC), including EPC‐A. Materials and methods: This retrospective multicentre study (2000–2025) included 25 HG‐EPC cases, irrespectively of ER/PR and HER2 status. Tumours with frank stromal invasion beyond microinvasive foci were excluded. Histopathological re‐evaluation was performed in accordance with 2019 WHO classification criteria. Results: Of 38 cases reviewed, 25 fulfilled the inclusion criteria as EPC (mean age 57.2 years, mean tumour size 2.9 cm). Six cases (24%) demonstrated conventional‐type microinvasive components. A subset of 16 cases fulfilled criteria for EPC‐A, defined by high‐grade morphology in combination with ER/PR‐negative (or ER n = 13) to pT1 ( n = 4) or pT2 ( n = 7), and pT3 ( n = 1). Adjuvant chemotherapy and radiotherapy were administered in 7 and 12 patients respectively. During follow‐up, four local recurrences (three invasive and one in situ ) were observed. One of the locally recurrent patients subsequently developed distant metastasis, and one breast cancer‐related death occurred 200 months after diagnosis. Recurrence or death occurred in 20% (5/25) of patients despite therapy. Microinvasion was seen only in the EPC‐A tumours. Conclusion: HG‐EPC and EPC‐A overlap morphologically and diagnostically with frankly invasive carcinomas and demonstrate a non‐negligible risk of recurrence. Clinical outcomes and more frequent microinvasion in EPC‐A support the view that EPC‐A is more appropriately regarded as an indolent form of invasive carcinoma rather than a purely in situ lesion and demonstrate a non‐negligible risk of recurrence and highlight the need for standardized staging criteria.

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