Assessment of tumor control following definitive radiotherapy in carcinoma of the prostate: A continuing dilemma

Evaluation of tumor response and tumor control after definitive radiotherapy is a relatively simple task in most malignancies arising at sites amenable to clinical examination (inspection and palpation). The rates of tumor regression following irradiation are quite variable. While some types of cancer regress completely during the radiotherapy course, some may take weeks or months to resolve. Occasionally, residual induration or a residual mass may persist for prolonged periods (many months), prompting the clinician to consider a biopsy for evaluation of the tumor status. In these circumstances histological examination may show necrotic tumor or residual fibrotic tissue. Finding viable-appearing tumor cells beyond the immediate postirradiation period (several weeks to a few months after completion of the radiotherapy course) is generally accepted as an equivalent of failure to eradicate the tumor. However, in a few types of cancer, presence of histologically identifiable and apparently viable tumor cells over protracted periods does not necessarily imply treatment failure