Tumor associated macrophages in human prostate cancer: relation to clinicopathological variables and survival.

Tumor associated macrophages (TAM) influence diverse processes such as angiogenesis, tumor cell proliferation, and metastasis during tumor progression. In a variety of tumor types, the amount of TAM has been associated with prognosis, but their role in prostate cancer has not been elucidated. The purpose of this study was to investigate the role of TAM in a series of 85 cases of prostatic carcinoma, diagnosed at transurethral resection of the prostate between 1975-1983, using immunohistochemistry and morphometrical techniques. Macrophage density was assessed as the maximum number of TAM per field in the three most macrophage dense areas (TAMmax) and as the average volume density of TAM in an estimate of the whole resected tumor. Furthermore, the individual cell profile area of TAM was assessed with an image analyzer. Macrophage variables were thereafter related to histological grade, tumor stage, metastasis as well as to vascular density, tumor cell proliferation and survival. Patients with a volume density of TAM in the fourth quartile had a shorter median cancer specific survival time than patients in the first to third quartile (3.3 vs. 5.9 years, p=0.005). Furthermore, an increased macrophage cell profile area was related to poor clinical outcome (4.6 vs. 5.9 years, p=0.039) whereas TAMmax gave no prognostic information. In a multivariate analysis, metastasis and the volume density of macrophages gave independent prognostic information (p=0.0008, p=0.010). However, when excluding metastasis from the analysis, only Gleason score was an independent predictor of cancer specific survival (p= 0.005). The volume density of TAM, the macrophage cell profile area and TAMmax increased with increasing Gleason score (p=0.001, p=0.0001, p=0.0001 respectively). A correlation was found between the volume density of TAM and tumor cell proliferation (rs=0.44, p=0.001) and an increased macrophage cell profile area was associated to microvessel density (rs=0.42, p=0.0001). Together these results suggest that both the functional state (as reflected by cell size), number and location of the macrophages are of importance for their influence on prostate tumors, but macrophage quantification is not a strong independent prognostic factor.