Evaluation of Mammographic Breast Density Effect of Aspirin: a Companion Study to Alliance Study A011502

• Must be either concurrently enrolling or previously enrolled to Alliance A011502. Eligible patients may be either pre- or post-menopausal.

• Patients must have either hormone receptor-negative breast cancer or be ER+ patients who have completed hormone therapy (e.g., tamoxifen, aromatase inhibitors) at least 6 months prior to registration to A011502.

• Patients must have baseline breast density measurement as defined by one of the following:

‣ \>= 25% breast density, or

⁃ Scattered areas of fibroglandular density, or

⁃ Breast composition category b, c, or d, per Breast Imaging Reporting and Data System (BI-RADS) 2013.

• Baseline digital screening mammogram (mediolateral \[MLO\] and craniocaudal \[CC\] views) taken prior to registration must be available for submission.

‣ For patients enrolling concurrently with Alliance A011502: Baseline digital screening mammogram must be taken within 8 weeks prior to registration to A211601. If a baseline mammogram within 8 weeks is not available, a new screening mammogram must be performed prior to treatment on Alliance A011502

⁃ For patients enrolling retrospectively: The patient's previous routine mammogram on file must be within 1 year prior to registration to A011502.

• Contralateral unaffected breast in place (with no prior cancer or radiation, no implants and no plan for breast surgery on contralateral breast over the course of the study). Patients with a prior biopsy on the unaffected breast are eligible.

• Not pregnant and not nursing.