The tumor microenvironment plays a critical role in cancer progression. Although its cellular and biochemical composition has been extensively studied, the impact of physical factors on tumor cell malignancy remains poorly understood. In ovarian cancer metastasis, tumor cells that spread to the coelomic cavity promote the secretion and accumulation of ascitic fluid (AF). Currently, the effect of the pH and the mechanical properties of this AF on metastatic progression are not well known. To advance our understanding of this problem, we employed both, biopsies from three patients (two with ovarian cancer and one with endometrial cancer that also had ovarian serous cysts) and, the ovarian cancer cell line SKOV3 as an in vitro model with HeLa cells as control to compare cell-type–specific responses to physicochemical cues. We then carried out histological, morphological and cellular analyses, and related the results to relevant clinical data.

First, we found that the AF from our patients have different densities and that the highest density AF contained the largest proportion of multinucleated tumor cells. Furthermore, SKOV3 cells treated with the high-density AF exhibited the largest number of multinucleated cells. Second, all AFs had an alkaline pH, ranging from 7.3 to 7.8. Although alkalinity did not correlate with the multinuclearity in the tumor cells present in AFs, it was significantly and positively associated with increased cell proliferation in both SKOV3 and HeLa cell lines.

Third, different densities of the AFs correlated with substantial morphological defects only in SKOV3 cells undergoing mitosis. This effect was mirrored by higher concentrations of soft agar without affecting HeLa cells.

We conclude that an alkaline pH and greater microenvironmental rigidity could enhance the metastatic potential of ovarian cancer cells. Thus, we propose that these two physical factors of the tumor microenvironment are parameters of clinical importance as predictors of malignancy.