Long‐term comparison of results of a drug sensitivity assay in vitro with patient response in lymphatic neoplasms

A short‐term differential staining cytotoxicity (DiSC) assay was used to assess the sensitivity of tumor cells in vitro from patients with chronic lymphocytic leukemia (CLL) and non‐Hodgkin's lymphoma to various cytotoxic drugs. The results have been correlated with drug sensitivities of the tumors in vivo. The chemosensitivity in vitro of eight patients with CLL was observed for 12 to 42 months. In 44 cases the assay correctly predicted seven sensitive and 30 resistant tumors (84% positive correlations). There were six false predictions of sensitivity and one false prediction of resistance. Repeated testing of patients receiving treatment revealed significant and progressive development of drug resistance, while serial tests on untreated patients with CLL gave unaltered results. The development of cross‐resistance to structurally related drugs was observed after treatment and many samples showed a high level of cross‐resistance. However, teniposide showed greater activity than etoposide, and mitoxantrone showed greater activity than the anthracyclines. The high level of agreement between laboratory and clinical results suggests that the DiSC assay may have a useful place (1) in guiding the clinician in the selection of drugs for chemotherapy and (2) in giving an added indication of prognosis for an individual with a lymphatic neoplasm.