Tumor cell proliferation and survival in patients with prostate cancer followed expectantly

Prostate cancers have different biological potentials, and aggressive tumors are difficult to identify when still localized. Tumor cell proliferation determined by MIB-1 expression has been suggested as an important predictor for outcome in several human cancers including the prostate. We test the possible prognostic value of tumor cellular proliferation in prostate cancer patients treated with no intent to cure.

Formalin fixed, paraffin embedded tumor tissue obtained at the time of diagnosis from 221 patients originating from a well known complete Danish prostate cancer population was immunohistochemically investigated. The tumor cell proliferation rate was determined using the MIB-1 antibody. Tumors were clinically localized in 57% of the patients.

Tumor cell proliferation rate expressed by the MIB-1 score significantly correlated with tumor stage (p <0.001) and malignancy grade (p <0.001). The MIB-1 score, divided into low and high by the median value, showed significant association with disease specific survival in the entire study population (p <0.0001), as well as in the 125 patients suffering from clinically localized disease (p=0.018). Multivariate analyses showed that MIB-1 was a significant (p=0.0003) prognostic factor in the entire population, including advanced disease stages. However, in the theoretically curable clinically localized subpopulation MIB-1 was not significant (p=0.08) contrary to histopathological grade (p=0.02), erythrocyte sedimentation rate (p=0.02) and T classification (p=0.035).

Prostate tumor cell proliferation, expressed by MIB-1 immunoreactivity, demonstrated significant association with disease specific survival. However, MIB-1 is a close alternative to histopathological grade in describing the natural history of clinically localized prostate cancer. The additional prognostic value and the practical consequence of tumor cell proliferation remain to be clarified.