9P - Clinicopathological features and prognosis of mucinous breast cancer: A retrospective analysis of 358 patients in Vietnam

Background

To evaluate clinicopathological features and prognosis in women with mucinous breast cancer (MBC), distinguishing between pure (PMC) and mixed (MMC) subtype.

Methods

A retrospective analysis of all 358 women with MBC treated at Vietnam National Cancer hospital from June 2015 to December 2020. PMC was defined by ≥ 90% mucinous components.

Results

We identified 358 women with MBC (245 PMC and 113 MMC) representing 2.7% of all 13,254 breast cancer patients. The proportion of stage I, II, III and IV were 34.9%, 50.8%, 10.4% and 3.9% respectively. 95.3% of patients were hormone receptor positive. The rate of HER2 overexpression is 12%, and only 1.4% of patients was treated with anti-HER2. 193 patients (53.9%) had chemotherapy (CT), including 55 patients (15.4%) treated in neoadjuvant setting. Among those received neoadjuvant CT, only 3 patients (5.5%) achieved pCR. Meanwhile, the rates of partial response, stable disease and progressive disease were 50.8%, 38.2% and 5.5% respectively. PMC patients were older (54.4±13.3 vs 51.1±13.1 years), had lower Ki67 expression, lower incidence of nodal metastasis (N+) than MMC patients (p values <0.05). At median follow-up of 58 months, the 5-year overall survival rate of non-metastatic patients was 86.6%. Univariate analysis revealed that significant factors for poorer OS were MMC subtype (p=0.02), large tumor size (T) (p<0.001), N+ (p<0.001), HER2 overexpression (p<0.001), PR negative (p=0.02), and high Ki67 (p=0.02). Multivariate analysis showed nodal metastasis (N+) to be the most significant prognostic factor (HR=3.3; 95%CI 1.5-7.1), followed by high T stage (HR=2.9; 95%CI 1.4-6.3), HER2 overexpression (HR=2.5; 95%CI 1.2-5.3) and MMC subtype (HR=1.9; 95%CI 1.0-3.9). Amongst 245 patients with stage T1-2N0M0, 40.8% of those treated with CT related to worse overall survival (5-year OS 88.0% vs 95.6%, p=0.04).

Conclusions

The majority of MBC are luminal subtypes and associated with good prognosis. Poor prognostic factors of women with MBC are high T, N stage, HER2 overexpression and MMC subtype. Chemotherapy in stage T1-2N0M0 brings a worse survival outcome compared to endocrine therapy. Given the low response rate to neoadjuvant CT, upfront surgery is appropriate for MBC patients.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.