QS19. ADH or DCIS? This is the question. Insights from a national multicenter study

Atypical ductal hyperplasia (ADH) is classified as a B3 lesion with uncertain malignant potential, sharing histological and architectural features with low-grade ductal carcinoma in situ (DCIS) but measuring less than 2 mm in extent. Surgical excision is recommended due to the risk of upgrade to DCIS or invasive carcinoma (IC). However, reliable predictors of upgrade have not been clearly identified due to the limited size and heterogeneity of published series. We gathered the first large multicentric cohort to evaluate predictive factors for upgrade and oncologic outcomes



Methods:

Data were collected from 6 Italian centers. Patients with a preoperative diagnosis of ADH on biopsy were included. Cases showing associated DCIS and/or IC were excluded.



Results:

Data from 855 patients treated between January 2010 and July 2025 were collected. Median age was 51 years (IQR 46-61) and 13 patients were male. Most cases (681/855, 77%) were screen-detected. Mammographic calcifications represented the most common radiologic finding (505/839, 60.2%), while non–mass-like enhancement was observed in 44/150 (29.3%) of cases undergoing contrast-enhanced mammography or magnetic resonance imaging. Breast conserving surgery was the predominant surgical approach: lumpectomy was performed in 524/855 cases (61.3%), while 284/855 (33.2%) underwent surgical biopsy. Mastectomy was performed in 42/855 (4.9%) cases and vacuum-assisted excision in only 5/855 cases (0.6%).

Following surgery, the pre-operative diagnosis of ADH was confirmed in 579/855 (67.7%) cases, while 276/855 (32.3%) were upgraded to IC (102) or DCIS (174).

Tumor size > 2 cm on imaging, apocrine differentiation, necrosis, presence of calcifications, and a time interval > 80 days between preoperative biopsy and surgery were significantly associated with upgrade.

After a median follow-up of 58 months, 13/855 (1.5%) patients experienced an invasive ipsilateral recurrence and 9/855 (1%) a DCIS ipsilateral recurrence. Four patients died during follow-up, one due to breast cancer.



Conclusions:

The 32.3% upgrade rate strongly supports surgical excision, both to exclude an associated malignancy and to confirm the histologic diagnosis. Tumor size, time interval between biopsy and surgery, and specific pathologic and imaging features were identified as predictive factors for upgrade.

ADH excision should not be delayed, as is commonly done for other B3 lesions, and cases showing predictive factors of upgrade should be surgically removed within two months to minimize the risk of an evolving underlying malignancy.