A small study has identified crizotinib as the culprit in reducing testosterone levels among men taking this drug as a treatment for anaplastic lymphoma kinase (ALK)-positive advanced non-small cell lung cancer (NSCLC).        

Andrew J. Weickhardt, MBBS, DMedSc, of the University of Colorado Cancer Center in Aurora, and colleagues sought to document the differences in testosterone levels between crizotinib-treated and non-crizotinib-treated men with metastatic NSCLC. As the researchers reported in the journal Cancer, total testosterone levels were low (<241 ng/dL) in all 19 men receiving crizotinib, compared with only 6 of 19 men (32%) not being treated with this oral ALK-directed tyrosine kinase inhibitor.

Only 1 in 5 patients who had ALK gene rearrangements and had not yet received crizotinib had low testosterone. Two patients who had previously had normal testosterone levels experienced rapid decreases in the hormone within 14 to 21 days of the initiation of crizotinib therapy. Luteinizing hormone and follicle-stimulating hormone levels also declined in those two men when crizotinib was administered. Discontinuation of the drug led to the restoration of normal testosterone levels.

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Low testosterone can reduce bone density, muscle strength, and sex drive and increase fatigue and depression. Because men may stay on crizotinib for months or even years, the effects of low testosterone could be profound.