Supplementary Material for: The Conundrum of Papillary Breast Lesions within the C3 Category

Objectives: To identify features that could define papillary ductal cell proliferation within the C3 category and to subcategorise papillary lesions into benign papillomas which can be managed conservatively and atypical/malignant papillary neoplasms which require surgical intervention. Study Design: A blind microscopic rescreen of all C3 cases was conducted. The corresponding histological outcome was compared with the cytology. Statistical analysis was performed using papillary versus non-papillary outcomes and benign versus atypical/malignant papillary lesions. In addition, macropapillary lesions (papilloma and encysted papillary carcinoma) were plotted against micropapillary ductal carcinoma in situ. Results: Two hundred thirty FNA cases reported as C3 included 72 papillary neoplasms (52 benign papillomas and 20 atypical/malignant papillary lesions). Features specific to papillary lesions within C3 include macropapillary fragments, complex sheets, palisading strips, cystic background, cohesion and a decreased nuclear-to-cytoplasmic ratio. Features favouring atypical/malignant papillary lesions include decreased numbers of bare bipolar nuclei, discohesion and a non-cystic background. These features are common to most breast malignancies; however, identification of papillary features often results in a downgraded diagnosis from C5. Conclusions: This study supports the ability to reliably identify papillary ductal cell proliferation within C3. Certain features can distinguish papillary lesions from other C3 pathologies. This separation is likely to be clinically useful as papillary lesions may require a different management approach.