Abstract P6-07-11: Is the prognosis of lymphotropic invasive micropapillary carcinoma worse than invasive ductal carcinoma?: A population-based study of 645 patients
Authors: Chen AC , Paulino AC , Schwartz MR , Rodriguez AA , Bass BL , Chang JC , Teh BS 
Published: August 2014

Abstract
Purpose: Invasive micropapillary carcinoma (IMPC) is an uncommon distinct variant of breast carcinoma and is associated with an increased risk for regional lymph node metastases. Therefore, IMPC is considered to have an unfavorable prognosis when compared to invasive ductal carcinoma (IDC). The prognostic factors for IMPC are not well characterized due to the relative scarcity of cases reported in the literature.
Methods: We analyzed the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database to evaluate prognostic factors of a population of 645 breast IMPC patients and 300,060 breast IDC patients reported between 2001 and 2008. Using univariate and multivariate analyses, hazard ratios (HR) were calculated for disease-specific (DSS) and overall survival (OS) for these patients using parameters such as patient age at diagnosis, histological grade, ER status, PR status, tumor size, and degree of lymph node positivity. Subset analysis of high grade, lymph node-positive patients was performed to compare DSS and OS between IMPC and IDC.
Results: The 5-year DSS and OS for IMPC patients were 92.1% and 84.6% compared to 5-year DSS and OS of 88.5% and 80.2% for IDC patients. At presentation, TNM staging of IMPC cases was similar to IDC except for a higher percentage of LN metastases (52.4% in IMPC vs. 34.7% in IDC). Of those with known estrogen receptor (ER) status, 84.2% of IMPC cases were ER-positive, which was associated with better DSS (Hazard Ratio (HR) 0.36, p &lt; 0.002) and OS (HR 0.62, p = 0.072). Patients with four or more positive lymph nodes had worse DSS (HR 7.1, p &lt; 0.0001) and OS (HR 3.2, p &lt; 0.0001) than node-negative patients, but those with one to three positive lymph nodes had similar DSS (HR 1.04, p = 0.96) and OS (HR 0.99, p = 0.97) as node-negative patients. In the subset of patients with high grade, node-positive breast carcinoma, patients with micropapillary histology had better DSS (p &lt; 0.03) and a trend towards better OS (p = 0.12) than high grade, node-positive invasive ductal carcinoma. This subset of IMPC patients also had a higher percentage of ER-positive tumors (77%) compared to IDC patients (56%).
Conclusions: While IMPC has a high propensity for lymph node metastasis, it has a disease-specific and overall prognosis that compares favorably to IDC. The higher percentage of hormone-receptor positivity may account for this survival advantage, even in high grade, node-positive disease. Therefore, estrogen-receptor-negativity or having four or more positive lymph nodes at presentation may potentially serve as prognostic markers for IMPC patients. In this study population, patients with one to three positive lymph nodes have DSS and OS similar to node-negative patients. Additional clinical studies are warranted to further investigate this observation. This is the largest study of IMPC to date, and these findings help our understanding of this uncommon histological variant of breast cancer.
Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-07-11.