Immunohistochemical localization of cathepsin B in neoplastic human prostate

Cathepsin B (CB) has been shown to degrade extracellular matrix (ECM) proteins, and has been reported to be involved in invasion and metastasis of several types of solid organ tumors in human and animals, but CB has not been studied in human prostate cancer (CAP). Our objective was to determine the CB protein immunostaining pattern in CAP and to correlate the immunostaining with the degree of malignancy as reflected in the Gleason grading system. We used two types of CB antibodies (namely, monospecific, polyclonal antibodies to human liver CB prepared in rabbits, and polyclonal antibody produced in sheep) to establish CB localization patterns in neoplastic prostate. Our analysis showed a heterogeneous CB immunostaining pattern in the neoplastic human prostate. CB immunostaining occurred in many, but not all, of the neoplastic columnar/cuboidal cells of acini and isolated cells, i.e., in small ragged glands and clusters (groups) of invasive cells in the prostatic stroma. We have shown that, in general, there was a positive correlation of the intensity of CB immunostaining with the Gleason histologic score (or Gleason grade sum) tumors, i.e., from the lowest scores through score 8, but many of the tumors with scores 9 and 10 showed little CB immunostaining. Our study indicated that the increased CB immunostaining in the Gleason grade sum 5–8 tumors may be associated with increased degradation of ECM, but not in 9 and 10 despite the fact that the latter tumors are more malignant clinically. In well‐differentiated tumors, fewer CB immunostaining cells were present than the moderately‐differentiated tumors. In other words, most of the stromal invasion of the prostatic ECM occurred in tumors of Gleason grade sums 5–8. We suggest that CB immunostaining might be a useful method to assess stromal invasion of prostatic carcinoma, especially in the higher grade tumors.