Differential levels of human leukocyte antigen-class I, multidrug-resistance 1 and androgen receptor expressions in untreated prostate cancer cells: The robustness of prostate cancer

Tumors are highly robust and maintain their proliferative potential against a wide range of both host-defense mechanisms and anticancer therapies. One of the approaches to overcome cancer robustness could be combined therapy in which each modality imposes independent selective pressures against the acquired mutation of cancer. To develop such a therapy, it is crucial to understand the magnitude of acquired mutations. In this study, we investigated the levels of human leukocyte antigen (HLA)-class I, multidrug-resistance 1 (MDR1), and androgen receptor (AR) expressions in untreated prostate cancers harvested by radical prostatectomy. The mean percentages of cancer cells expressing HLA-class I, MDR and AR among the 10 cancer samples were 41, 35 and 74%, respectively. In addition, double-staining of HLA and MDR revealed the four definite populations (HLA⁺/MDR⁺, HLA+/MDR^-, HLA-/MDR⁺and HLA^-/MDR^-) in cancer tissues from the majority of cancer patients tested, and the mean percentages of cells expressing these combinations were 13, 29, 22 and 38%, respectively. Similar results were obtained by double-staining of HLA and AR, except for 2 cases in which HLA ^-/AR⁺cancer cells predominated. These results indicated that untreated prostate cancer cells acquired a wide range of genomic mutations, which may have been caused by internal host pressure to eliminate malignant cells, and would provide evidence of the robustness of untreated prostate cancer.