Evaluation of Neoadjuvant Treatment Response in Rim Enhancing Cystic Appearing Breast Cancer

Purpose: Response to neoadjuvant chemotherapy (NAT) is based upon measuring the tumor’s longest diameter according to the Response Evaluation Criteria in Solid Tumors (RECIST). When rim-enhancing lesions are encountered, especially those with cystic appearance, RECIST assessment might be challenging in terms of employing rim thickness, longest diameter, or both as the target metric. We aimed to explore the relationship between rim thickness and longest diameter with cancer pathological subtypes in order to set recommendations for appropriate measurements.

Methods: We reviewed Dynamic MR Images of 22 cases of rim-enhanced cystic appearing invasive ductal carcinoma (IDC) before and during NAT. Early and delayed rim and central zone enhancement and T2 signal intensity were evaluated and compared to pathology subtypes.

Results: The cohort included 5 cases of HER2-enriched and 17 cases of triple-negative (TN) tumors. HER2-enriched tumors were found to have a thicker rim, delayed central zone enhancement and non-homogenous T2 signal. TN tumors demonstrated very thin rim enhancement or mixed rim thickness and bright T2W central zone with negligible enhancement, generating a cystic appearance. The differences in enhancement patterns between the two subtypes were statistically significant (p=0.016). Response to NAT exhibited a reduction in the longest diameter in similar fractions in both subtypes. Decreased rim thickness was more frequent in the TN than in HER2-enriched tumors. Two cases demonstrated mixed response with thinning of the rim yet stable longest diameter.

Conclusions: Rim-enhancing and cystic appearing breast cancer can be seen in TN and HER2-enriched tumors. Both rim thickness and longest diameter are tumor-specific. For NAT response assessment, we recommend the longest diameter as target lesion measurement. Rim thickness changes should be additionally reported as part of the tumor description.