Human tumor clonogenic assay in patients with unknown primary carcinomas.

The Human Tumor Clonogenic Assay (HTCA) was used in patients with unknown primary carcinomas (UPC) to evaluate chemosensitivity in vitro for this patient group and to possibly aid in the selection of chemotherapy for clinical trial. A total of 178 drug assays including 15 standard and 13 experimental anti-cancer drugs were performed on tumor cells from 19 patients. A median of six drugs were studied in vitro per patient. Sensitivity was noted in only 3.4% of the studies (six drug assays). The marked in vitro pattern of resistance observed with UPC correlates well with the known clinical experience with this entity. Ten patients were evaluable for clinical correlation of response between in vitro and in vivo sensitivity; however, many received drug combinations and not all the drugs had been tested in vitro. One of six evaluable patients exhibiting in vitro sensitivity and one of four with in vitro resistance achieved remission. Additional single-agent in vitro/in vivo correlations will be needed to establish whether HTCA will have any future impact in the treatment of patients with UPC. A more promising application of HTCA for UPC would appear to be as an aid in screening and discovery of new drugs of potentially greater efficacy for this resistant tumor category.