Can tumour response be assessed from a biopsy?

During a course of radiotherapy or chemotherapy the number of clonogenic cells in a tumour decreases exponentially. After one third of the treatment period more than 99% of the remaining tumour consists of doomed cells. Therefore, it would appear to be impossible to assess the therapeutic response of tumours directly from biopsy material taken during treatment. Nevertheless, attempts to study the therapeutic response during treatment have been made in order to obtain prognostic information on individuals so as to individualize treatment. A variety of approaches have been used. In carcinoma of the cervix a close correlation has been established between the results of some of these assays and local tumour control or long term survival of patients. Even without a complete understanding of the undelying mechanisms, these methods may be useful for the selection of patients for unconventional treatments like fast neutrons or other modalities which are not available to all patients.