A study from Quest Diagnostics medical experts shows how a lab-developed test could help assess levels of several tamoxifen drug metabolites in a blood specimen. The study, "A Novel Commercial LC-MS/MS assay for Tamoxifen (TAM) and its Major Metabolites," evaluated the blood serum from 155 women who were on 20 mg/day tamoxifen for more than 6 months. The patient population exhibited a wide range of concentrations of TAM and its metabolites during therapy, reflecting individual differences in the ability to metabolize the drug. The study was presented on Dec. 11 at the 2015 San Antonio Breast Cancer Symposium in San Antonio, TX.
This research is important because separate studies show tamoxifen, taken for 5 years, reduces the risk of developing invasive breast cancer by about 50 percent in postmenopausal women who are at increased risk of getting the disease. However, compliance is an issue and patients could be further helped from precise prescribing - side effects from Tamoxifen are known to include mood swings, depression, and loss of libido, cataracts, blood clots, strokes, bone loss and the increase risk of endometrial and uterine cancer.
Five years of therapy with tamoxifen has been the standard of care for women with early stage, ER-positive breast cancer following "curative" surgery. While tamoxifen can significantly reduce the risk of recurrence, differences in how women metabolize the drug, due to gene variants or other drugs (i.e., SSRIs for depression), may influence its effectiveness in preventing a return of cancer.
Quest Diagnostics recently introduced the test that helps physicians quantify the level of tamoxifen drug metabolites in the blood stream. Based on a tandem mass spectrometry, a technique used by world-class laboratories to measure hormones and vitamin D, the test allows physicians - for the first time - to employ a commercially available therapeutic drug monitoring approach for their tamoxifen-treated patients. The test may also help physicians assess noncompliance with tamoxifen therapy, a common problem given side effects such as weight gain or loss.
When people think of "personalized medicine" or "precision medicine" they often think of genetic testing to assess a drug against a gene variant. But a growing area in personalized medicine is the use of qualitative enzyme or drug metabolite testing to assess the biological impact of a drug rather than the indirect influence of genes.
Nigel Clarke, Ph.D., co-author and a senior scientific expert responsible for technology innovation for Quest Diagnostics, leads innovations in therapeutic drug monitoring based on these types of tests.