Micropapillary pattern in pure mucinous carcinoma of the breast - does it matter or not?

Pure mucinous carcinoma (PMC) of the breast is a low-grade cancer. In this study, we aimed to elucidate the prognostic significance of micropapillary structures in breast PMC.

Seventy-five patients with breast PMC were recruited. All haematoxylin and eosin (H&)-stained slides were reviewed, and clinicopathological features including age, tumour size, growth pattern, nuclear grade, histological grade, lymph node (LN) status, immunohistochemistry (IHC) staining of hormone receptor, human epidermal growth factor receptor 2 (HER2) expression and Ki-67 proliferation index were analysed. Fluorescence in-situ hybridisation (FISH) was used to verify the amplification of the HER2 gene in IHC 2+ cases. Seventy-one cases of PMC were followed-up from 18 to 110 months (median = 68 months). All PMC patients were female, aged 31-83 years (median = 57 years). All PMCs were nuclear grades 1 or 2. Oestrogen receptor was positive in all cases (100%) and progesterone receptor was positive in 68 cases (90.7%). There was no 3+ staining or gene amplification of HER2. Four patients had axillary LN metastasis (5.7%). Micropapillae were observed in 60 cases (80%) with varied percentages, and divided into five groups: 0%, <20%, 20-49%, 50-89% and ≥90%, with 15 (20%), 15 (20%), 17 (22.7%), 17 (22.7%) and 11 (14.7%) cases in each. Follow-up results showed that neither recurrence nor distant metastasis occurred in all PMCs. Statistical analysis revealed that only larger tumour size was correlated significantly with LN metastasis (P < 0.05).

The presence of nuclear grades 1 or 2 micropapillae, irrespective of the percentage, had no significant relationship with LN metastasis and patients' survival of PMC.