Lack of attenuation in the antitumor effect of tamoxifen by chronic CYP isoform inhibition.
Tamoxifen is a selective estrogen receptor modulator used in estrogen receptor-positive breast cancer. Tamoxifen is metabolized to an extremely potent antiestrogen by cytochrome P450 (CYP) 2D6, 2C9, and 3A isoforms. The selective serotonin reuptake inhibitors (SSRIs) are potent inhibitors of these CYPs. Since the prevalence of depression in breast cancer patients is nearly triple that of the general population, it is likely that a subgroup of breast cancer patients will receive long-term treatment with both an SSRI and tamoxifen. A case control design was used to investigate the possibility that a resultant decrease in production of the 4-hydroxy metabolite from chronic inhibition results in the attenuation of the antitumor effect of tamoxifen. Twenty-eight patients without recurrences of breast cancer (controls) were matched to an equal number of cases (recurrences) by cancer stage and year of diagnosis. Data were analyzed on all chronic medication exposure (> 3 months) in both cases and controls classified as to their status as CYP 2D6, 2C9, and 3A inhibitors, substrates, or inducers. No significant difference was found for CYP inhibitor or substrate exposure between cases and controls. Indeed, controls showed a slightly greater exposure to inhibitors of the relevant CYP isoforms compared to cases. These results suggested a trend toward the null hypothesis. It is unlikely that the effect of chronic exposure to potent CYP isoform inhibitors affects the antitumor effect of tamoxifen and its 4-hydroxy metabolite, supporting the safety of the continued practice of concomitant SSRI administration to breast cancer patients with depression.
Lehmann
David
D
SUNY Upstate Medical University, Syracuse, USA.
Nelsen
Jamie
J
Ramanath
Vijay
V
Newman
Nancy
N
Duggan
David
D
Smith
Adrienne
A
D018687:Antidepressive Agents, Second-Generation / Q000378:metabolism / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000378:metabolism / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D016022:Case-Control Studies; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D004791:Enzyme Inhibitors / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D017367:Selective Serotonin Reuptake Inhibitors / Q000378:metabolism / Q000627:therapeutic use; D013629:Tamoxifen / Q000378:metabolism / Q000627:therapeutic use*; D016896:Treatment Outcome
D018687:Antidepressive Agents, Second-Generation; D000970:Antineoplastic Agents; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D017367:Selective Serotonin Reuptake Inhibitors; D013629:Tamoxifen