In a 72-year-old patient with a history of estrogen-sensitive breast cancer who is interested in testosterone therapy for libido and muscle support, what laboratory tests should be ordered?

Do Not Prescribe Testosterone to This Patient

Given this patient's history of estrogen-sensitive breast cancer, testosterone therapy is contraindicated and should not be pursued. The Endocrine Society explicitly recommends against generalized testosterone use in women due to inadequate indications and lack of long-term safety data 1, and this is particularly critical in a patient with hormone-sensitive malignancy.

Why Testosterone is Contraindicated Here

Breast Cancer Risk with Testosterone

• Testosterone converts to estradiol through aromatization, which directly stimulates estrogen-sensitive breast tissue 2
• While androgens may oppose estradiol-induced proliferation in some contexts 1, the conversion pathway creates unacceptable risk in estrogen-receptor-positive breast cancer survivors
• The FDA labeling for testosterone products does not address use in women with breast cancer history, and breast cancer is generally considered a contraindication 3

Lack of Evidence for Safety and Efficacy

The Endocrine Society's 2006 guideline is unequivocal 1:

• No diagnosis of "androgen deficiency" should be made in women - there is neither a well-defined clinical syndrome nor normative testosterone data across women's lifespans
• Recommend against generalized testosterone use due to inadequate indications and lack of long-term safety evidence (beyond 24 weeks)
• Safety data specifically regarding breast effects are insufficient, with recommendations that future studies should measure effects on breast tissue including mammographic density and markers of cell proliferation 1

If You Were to Consider Labs (Which You Should Not Order)

Since testosterone therapy should not be prescribed, ordering labs would be inappropriate and potentially misleading. However, for educational purposes, if this were a patient without breast cancer history being evaluated, the Endocrine Society recommends 1:

• Total testosterone (though current assays lack adequate sensitivity for female ranges)
• Free testosterone (even more problematic to measure accurately in women)
• SHBG (sex hormone-binding globulin)
• Fasting lipid profile
• Fasting glucose and insulin
• Liver function tests

But again: these labs should not be ordered for this patient because testosterone therapy is not an option.

Alternative Approaches to Address Her Concerns

For Libido Issues:

• Evaluate for other causes: relationship factors, medications (SSRIs, antihypertensives), depression, anxiety
• Consider non-hormonal interventions: pelvic floor physical therapy, sexual counseling
• Assess for vaginal atrophy if present (ultra-low-dose vaginal estrogen may be considered with oncology consultation)

For Muscle Support:

• Resistance training is evidence-based and safe
• Adequate protein intake (1.2-1.6 g/kg/day)
• Vitamin D optimization
• Rule out other causes of muscle loss: thyroid dysfunction, vitamin B12 deficiency, deconditioning

Critical Pitfall to Avoid

Do not be swayed by the recent small retrospective study 2 showing symptom improvement with testosterone in breast cancer survivors. This was an open-label, uncontrolled study of only 47 women with high risk of bias. It cannot override:

• The lack of long-term safety data
• The biological plausibility of harm through estradiol conversion
• The explicit guideline recommendations against use
• The absence of FDA approval for this indication

The potential mortality risk from breast cancer recurrence far outweighs any quality-of-life benefits from testosterone therapy in this population.