Aromatase Inhibitor Host Factors Study

The available evidence suggests that circulating estradiol levels play a critical role in determining effectiveness of aromatase inhibitor therapy, and that maximal suppression of aromatase activity and estrogen production is essential for optimal disease control. Host factors such as high 25-Hydroxy Vitamin D (25-OH D) levels and obesity, which might increase residual estrogen levels, could adversely impact outcome and lead to an increased risk of recurrence or death. The primary objective of Part A (which includes women regardless of BMI) is to directly evaluate the relationship between (i) 25-OH D levels and serum estrogen levels and (ii) BMI and serum estrogen levels in a cohort of postmenopausal women on standard dose letrozole therapy (2.5 mg/day). Part B (which includes only women with BMI > 25 kg/m2) will determine whether an increased dose of letrozole (5 mg/day), which had no dose limiting side effects in a Phase I study improves suppression of estrogen in overweight/obese women.

Inclusion criteria

• Postmenopausal female patients
• histological confirmed diagnosis of estrogen receptor and/or progesterone receptor positive breast cancer (Stage I-III) who have completed local therapy
• Currently prescribed and taking letrozole 2.5 mg daily for a minimum of 3 months
• Willing to provide written informed consent to participate
• for the experimental arm: all of the above and body mass index (BMI) > 25 kg/m2

Exclusion criteria

• Known abnormal liver or renal function defined by:

• Serum Creatinine > 1.25 times institutional upper limit of normal (ULN) or Calculated Creatinine Clearance < 40 mL/min
• Serum Bilirubin, Aspartate transaminase (AST) or alanine transaminase (ALT) > 1.5 times ULN
• Presence of persistent local or known metastatic cancer