A comparison of the imaging features of pleomorphic and classical invasive lobular carcinoma

Purpose: Pleomorphic invasive lobular carcinoma (pILC) is a distinct morphological variant of ILC with a poorer prognosis than classical ILC (cILC). The aim of this study was to ascertain whether the conventional imaging appearances of the two entities differ.

Methods: A single-center retrospective review of conventional imaging was undertaken in 150 consecutive patients with histopathologically confirmed ILC (38 pILC; 112 cILC) between April 2010 and July 2015. Mammographic and sonographic findings were evaluated using the BI-RADS lexicon by a radiologist blinded to pathology, and the findings in the two groups were compared. The degree of discrepancy between imaging and pathological sizing in the two groups was evaluated.

Results: Lesions were mammographically occult in 11% of pILC and 14% of cILC (p = 0.56). On mammography, skin or trabecular thickening and microcalcification were commoner in pILC than cILC (13% vs. 1%, p < 0.01; 25% vs. 5%, p < 0.01). Architectural distortion was more frequent in cILC than pILC (26% vs. 9%, p = 0.01). On ultrasound, pILC more frequently exhibited mixed echogenicity (28% vs. 13%; p = 0.04), skin thickening, subcutaneous or parenchymal edema (8% vs. 0%; p = 0.02), echogenic surrounding fat (33% vs. 9%; p < 0.01), and posterior acoustic enhancement (10% vs. 1%; p = 0.02) than cILC. CILC was more frequently manifested as a focal area of altered echogenicity (24% vs. 8%; p = 0.04). Mean elastography stiffness was higher for pILC (174.8 vs. 124.6 kPa; p = 0.02). Imaging-pathological size disparity was similar for both subtypes.

Conclusion: There are differences in the imaging features between pILC and cILC which reflect the more aggressive nature of pILC.