RETINOIDS IN CANCER-THERAPY

Purpose: Recent reports of the dramatic antitumor effect of all-trans retinoic acid (RA) in patients with acute promyelocytic leukemia (APL) have generated renewed enthusiasm for clinical studies of retinoids for oncologic therapeutic indications. Here we provide an overview of relevant aspects of retinoid physiology and molecular biology, review preclinical studies indicating antitumor activity for retinoids, and summarize the current status of clinical investigations of retinoid use for the treatment of adult and pediatric tumors. Design: The published literature was reviewed with attention to areas of retinoid research that would shed insight into the oncologic uses of retinoids. Results: Retinoids play critical roles during normal fetal development and induce differentiation (and/or growth inhibition) in a variety of tumor-cell lines. Retinoid effects seem to result from changes in gene expression mediated via specific nuclear receptors (termed retinoic acid receptors, RAR-α, -β, and -γ), and a specific chromosomal translocation involving the RAR-α gene occurs in APL patients. In addition to the very high clinical response rate for RA in patients with APL, significant clinical responses have been observed for patients with cutaneous T-cell malignancies, juvenile chronic myelogenous leukemia, and dermatologic malignancies. Additionally, the combination of 13-cis-retinoic acid (cRA) with interferon alpha (IFNα) has produced high objective response rates for patients with squamous cell carcinomas of the head and neck and of the cervix. Conclusions: The antitumor activity demonstrated for retinoids (especially RA) alone and in combination with other agents supports the need for targeted phase II trials to define the spectrum of responsive tumors and for laboratory studies to further delineate the biologic mechanisms associated with therapeutic responses. High priority should then be given to phase III trials to delineate optimal strategies for improving outcome by combining retinoid-based treatments with conventional chemotherapy and radiotherapy regimens.