MenaINV Isoform Expression in Human Invasive Ductal Carcinomas of the Breast Correlates with Tumor Microenvironment of Metastatsis (TMEM) Score; a Pilot Study Indicating the Potential Use of MenaINV/11a Ratio as a Predictor of Distant Metastases.

Abstract

Abstract Background: Primary mammary carcinomas in rodents contain a subpopulation of invasive tumor cells that move towards perivascular macrophages and intravasate. An isoform of actin regulatory protein Mena, MenaINV is up-regulated in these invasive cells, while isoform Mena 11a is down regulated (Goswami et al 2009). The direct apposition of Mena positive tumor cells to endothelial cells and perivascular macrophages has been described as Tumor Microenvironment of Metastasis (TMEM) and its density is shown to be a predictor of metastatic outcome in human invasive ductal carcinomas of the breast (Robinson et al 2009). We questioned if MenaINV and Mena 11a isoform expression correlates with the invasiveness of breast lesions in Polyoma Middle T antigen (PyMT) mouse mammary tumors and human invasive ductal carcinomas (IDC), as well as if increased MenaINV expression is associated with high TMEM counts in human IDCs.Materials and Methods: We analyzed MenaINV and Mena 11a expression in fine needle aspiration biopsy (FNA) samples from 18 mice with PyMT mammary tumors, 3 human IDCs and 1 fibroadenoma (FA) by qRT-PCR. The expression of Mena isoforms from in situ PyMT lesions was compared with metastatic PyMT tumors and expressed as fold change. Mena isoform levels from IDC were compared to that in FA and expressed as fold change. Representative sections from IDCs were triple immunostained with anti-Mena, anti-CD 68 and anti-CD34 and independently analyzed for TMEM counts on ten x400 fields by two pathologists.Results: We observed a 7.5 fold increase in MenaINV expression and a 3 fold decrease of Mena 11a in metastatic PyMT tumors when compared to in situ lesions. The results from human samples are shown in Figure 1. The top panel shows MenaINV and Mena 11a fold change in IDCs compared to FA. The bottom panel shows TMEM counts for each IDC and MenaINV/11a ratios. Both, MenaINV expression and TMEM count varied significantly, whereas Mena 11a was exceedingly low in IDCs. In all 3 IDCs the levels of MenaINV correlated with TMEM counts.Discussion: This pilot study indicates for the first time that the expression of MenaINV and Mena 11a can be successfully analyzed in FNA biopsy samples from human breast lesions. In combination with the TMEM count, Mena isoforms can potentially become useful markers for predicting the metastatic potential of an individual breast lesion. A larger study is underway to develop a scoring system combining Mena isoform expression with the TMEM count.Figure 1: Top panel: qRT-PCR assessment of Mena splice variant expression in FNA samples from human breast lesions. Levels of MenaINV and Mena 11a in 3 IDCs were compared to those in FA. The result is expressed as fold change. Bottom panel: TMEMs on tissue sections from IDC with TMEM counts and MenaINV/11a ratios. Circles represent TMEMs. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2140.