Breast hamartomas associated with epithelial atypia and malignancy: are there specific clinical, radiological or pathological features that identify at risk patients?

Purpose: Breast hamartomas are rarely associated with epithelial atypia or malignancy. Since the introduction of digital mammography in the UK from 2008, hamartoma detection has increased. The aim of this study was to identify if there are characteristic clinical, radiological or histological features that distinguish hamartomas with intralesional atypia/malignancy (complex hamartomas, CH) or ipsilateral/contralateral atypia/malignancy (non-CH) from those without atypia/malignancy at diagnosis (other benign hamartomas, BH).

Methods: We performed a retrospective single-institution review of 450 hamartomas reported between 2010 and 2023. Anonymised H&E sections and imaging of CH and non-CH were reviewed to identify distinguishing features.

Results: 13,441 benign breast lesions were biopsied/resected between 2010 and 2023 including 450 hamartomas (3.3%), 19 of which (4.2%) were associated with atypia or malignancy. 14 were analysed further (7 CH; 7 non-CH). The mean age of CH plus non-CH patients was significantly higher than patients with BH (47.5 vs. 40.6 years; p = 0.03). The mean size of CH was greater than non-CH (32.1 mm vs.17.6 mm; p = 0.06). There was a statistically significantly higher incidence of atypical/malignant lobular lesions (ALH/LCIS/ILC) in CH vs. non-CH (42.9% vs 0%; p = 0.05). MRI was performed in 2 CH and 3 non-CH; in all 5 the associated malignancy was detected. There was no significant difference between the CH and non-CH group in ultrasound/mammographic features, other hamartoma histological features or other associated benign breast changes.

Conclusions: Ultrasound/mammogram are not sufficiently sensitive to identify hamartomas with associated atypia/malignancy. Certain hamartoma features may preferentially be associated with atypia/malignancy and which merit further radiological and/or detailed histological investigation.