The aim of this study was to characterize phenotypic alterations along the progression of
breast carcinoma from primary
tumor to
pleural effusion through analysis of the expression of
nerve growth factor (
NGF) and its receptors phospho-TrkA (p-TrkA activated receptor) and p75. Sections from 42
malignant pleural effusions from
breast cancer patients and 65 corresponding solid
tumors (34 primary, 31 metastatic) were evaluated for
protein expression of the activated p-
TrkA receptor. The majority of lesions were additionally studied for
NGF and p75 expression. Six effusions and four
breast carcinoma cell lines were studied for expression of p-TrkA using immunoblotting (IB). Membrane expression of p-TrkA was high in
carcinoma cells in effusions (39/42, 93%) and locoregional recurrences (12/13, 92%), with significantly lower expression in both primary
tumors (14/34, 41%) and
lymph node metastases (8/18, 44%), respectively (p < 0.001 for effusions vs. primary
tumors; p = 0.001 for effusions vs. lymph nodes). In contrast, p75 expression was less frequent in effusions compared to both primary
tumors and
lymph node metastases, significantly so for the latter (p = 0.019).
NGF expression was comparable at all sites, but its expression in
tumor cells in effusions (7/21 cases) was limited to cases in which time to progression (
TTP) to effusion occurred within 5 years or less from primary operation. In univariate analysis of survival, mean and median
TTP were 6.3 and 6 years for
NGF-negative effusions, compared to 3 and 4 years for
NGF-positive cases (p = 0.013). IB confirmed expression of p-TrkA in five of six effusions, while all four
breast cancer cell lines were p-TrkA-negative. Our data provide the first documented evidence of molecular events that occur along
tumor progression of
breast carcinoma from primary
tumors to effusion. The almost universal expression of p-TrkA in
cancer cells in effusions and late recurrences is in full agreement with our recent report linking this factor with poor prognosis in
ovarian cancer. Furthermore, the rapid progression to effusion in cases showing
NGF expression in
tumor cells underscores the aggressive clinical behavior of
tumors that are able to utilize this pathway in an autocrine manner.