Inclusion Criteria

DISEASE CHARACTERISTICS:

- 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

PATIENT CHARACTERISTICS:

- 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)