Eradication of prostatic high grade intraepithelial neoplasia: Hypothesis and clinical proof

Abstract

1534 Background: Recently normal prostate tissue has been found to contain a high concentration of retinoid X receptors (RXRs), they are found in the highest concentrations in ectodermal tissue. Loss of these receptors is associated with prostatic intraepithelial neoplasia (PIN), and can be present in patients with a normal PSA. There are 115,000 cases of high grade PIN discovered yearly in the United States.The drug bexarotene used to treat cutaneous T cell lymphoma (CTCL). The compound is not a true retinoid in structure, perusal of the structure reveals two aromatic rings one of which contains a carboxy group which would make one anticipate strong hydrogen bonding when it undergoes binding to the RXRs as if it were a retinoid, resulting in “up regulation” of the tissue with increase in differentiation to normal tissue. Based upon this it was felt that it would be fruitful to try bexarotene in High Grade PIN. Method: The diagnosis was based upon 12 biopsies which were done in conjunction with ultrasound localization of the biopsy site, with careful recording of there anatomical position. The patient was started on bexarotene 225 mg per day. The drug was given as a single dose once daily; this dose is 40% of the dose normally used to treat CTCL. The drug was administered for 30 doses During the period of therapy the patient was on Atorvastin T4 total was within the normal range. Results: Four weeks following the last dose of bexarotene the prostate was rebiopsied with 12 biopsies taken. Six of the biopsies were taken from the putative area, the rest in an enlarging target like pattern. The repeat biopsy was negative for the presence of PIN. 14 months later 12 more biopsies were obtained using the same technique, these repeat biopsies were also found to be negative; ie. 24 negative biopsies over 14 months. It is unlikely that the previously involved area was missed. Conclusion: If a mechanism of action were to be formulated, the induction of and increase in RXRs in normal prostate cells would be reasonable. Cells that undergo the formation of PIN, strong hydrogen bonding and inability of those cells to produce more receptors could result in apoptosis. Undoubtedly further study is required to evaluate the effect of this drug in high grade PIN. No significant financial relationships to disclose.