- To assess the operating characteristics of the ¹³C-dextromethorphan (^13 C-DM) breath test in identifying women with breast cancer (or at high risk) who are CYP2D6-genotypic poor metabolizers.
- To examine the correlation between CYP2D6 enzyme activity (as measured by the breath test) and plasma endoxifen (and 4-hydroxyTAM) levels in patients who carry one or more CYP2D6 functional alleles.
- To examine the change in CYP2D6 enzyme activity (as measured by the ¹³C-DM breath test), in patients who start a CYP2D6 inhibitor while taking tamoxifen.
- To determine whether CYP2D6 enzyme activity (as measured by the breath test) changes over time (either as a consequence of drug-induced inhibition or other).
- To measure genetic variation in additional genes that are later identified to affect the metabolism, uptake, or distribution of tamoxifen (e.g., SULT1A1, UGT).
OUTLINE: Patients receive tamoxifen citrate for 6 months. ^13C-dextromethorphan breath tests are conducted at baseline and periodically during the 6 months.
13C-dextromethorphan breath test: Patients receive oral Alka-Seltzer® Gold (ASG; citric acid, potassium bicarbonate, and sodium bicarbonate) in water, then, 15 minutes later, another ASG dose and oral ¹³C-dextromethorphan. Patients breathe into a bag 1-2 times, and the is bag sealed. ¹³CO_2 levels in the bags are measured.
Blood samples are collected at baseline and periodically for pharmacogenetic and pharmacokinetic studies by reverse phase HPLC with fluorescence detection.
After completion of study therapy, patients are followed annually for 5 years.
- Eligible to receive tamoxifen for 6 months for either the prevention or treatment of non-invasive or invasive, stage I-III breast cancer
- CYP2D6 genotype known
- Patients determined to be CYP2D6 poor metabolizers (by determination of a genotype test by their Mayo physician prior to study registration) are eligible to proceed with the initial breath test only
- Hormone receptor status not specified
- Menopausal status not specified
- ECOG performance status 0-2
- Life expectancy > 6 months
- No known impaired hepatic activity defined as ≥ grade 3 AST, alkaline phosphatase, or total bilirubin
- No pulmonary disease (e.g., asthma or other respiratory disease) associated with hypercapnia
- No uncontrolled metabolic disease (e.g., diabetes in the presence of gastroparesis, uncontrolled congestive heart failure, or uncontrolled gastrointestinal disorders [e.g., GERD])
- No prior adverse reaction to dextromethorphan
- No history of chronic liver disease (e.g., hepatitis B or hepatitis C, alcoholic liver disease, cirrhosis, or fibrotic disease)
- Able and willing to fast overnight prior to the study session
- Willing to return to Mayo Clinic for follow-up
- Willing to provide biologic specimens
PRIOR CONCURRENT THERAPY:
- More than 24 hours since prior medications known to slow gastric emptying or gastrointestinal motility (e.g., alcohol, opioid analgesics, anticholinergics [e.g., antihistamines], and loperamide)
- More than 4 weeks since prior and no concurrent CYP2D6 inhibitors or concurrent serotonin-reuptake inhibitors known to be potent CYP2D6 inhibitors (e.g.,paroxetine [Paxil®] and fluoxetine [Prozac®]
- If mild to moderate inhibitors of CYP2D6 are medically necessary, patients may go back on after the 8-week time point
- More than 4 weeks since prior and no concurrent monoamine-oxidase inhibitors (e.g., furazolidone, phenelzine, procarbazine, selegiline, and tranylcypromine)
Last updated: 12/28/2011