This phase II trial is studying vitamin D deficiency, muscle pain, joint pain, and joint stiffness in postmenopausal women receiving letrozole for stage I-III breast cancer. Learning about vitamin D deficiency and muscle pain, joint pain, and joint stiffness in patients receiving letrozole for breast cancer may help doctors plan treatment and may help patients live more comfortably

PRIMARY OBJECTIVES:

I. To assess the rate of vitamin D deficiency in breast cancer patients who experience myalgias, arthralgias and/or joint stiffness following initiation of adjuvant letrozole treatment.

SECONDARY OBJECTIVES:

I. To determine if there is a correlation between letrozole serum levels and the development of myalgias, arthralgias and/or joint stiffness.

II. To assess if vitamin D supplementation may alleviate myalgias, arthralgias and/or joint stiffness associated with letrozole in those subjects with vitamin D deficiency.

OUTLINE:

Patients receive letrozole orally (PO) once daily (QD). Patients, who experience muscle pain, joint pain, or joint stiffness that requires an intervention and who are found to be vitamin D deficient, also receive calcium PO and vitamin D3 PO. Treatment continues for up to 28 weeks in the absence of disease progression or unacceptable toxicity.

Inclusion Criteria:

• Patients must have a histologically confirmed diagnosis of Stage I, II or III breast carcinoma
• Patients must be prescribed letrozole for adjuvant breast cancer treatment
• Prior adjuvant tamoxifen is permitted
• Patients must be postmenopausal; for study purposes, postmenopausal is defined as: a prior documented bilateral oophorectomy, or a history of at least 12 months without spontaneous menstrual bleeding, or have a persistently postmenopausal estradiol in the past 6 months without menses, and clinically in menopause at the judgment of the treating physician, or age 60 or older with a prior hysterectomy without oophorectomy, or age less than 60 with a prior hysterectomy without oophorectomy (or in whom the status of the ovaries is unknown), with a documented FSH level demonstrating confirmatory elevation in the postmenopausal range for the lab

Exclusion Criteria:

• Diagnosis of Stage IV breast carcinoma
• Pre-existing myalgias, arthralgias and/or joint stiffness >= Grade 1, as defined using CTEP CTC identified during baseline physical exam
• Inability to understand or cooperate with study procedures
• Receipt of investigational drug within 30 days before study entry
• Lack of physical integrity of the upper gastrointestinal tract or malabsorption syndrome
• Unwillingness to give informed consent
• Unwillingness to participate or inability to comply with the protocol for the duration of the study
• Patients with serum calcium >= 14 mg/dL
• Patients with renal dysfunction defined as glomerular filtration rate <10ml/min calculated using Cockroft-Gault equation