Fish oil may ease joint pain from breast cancer pills

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria * Female subject aged ≥ 18 years who are postmenopausal according to standard clinical criteria or who will have been receiving LHRH agonist therapy for at least 28 days prior to AI initiation. * Stage 0-3 estrogen receptor positive (≥1%) and/or progesterone receptor positive (≥1%) breast cancer, or patients at high risk of developing breast cancer who are planning to initiate AI therapy for chemoprevention. * Planned initiation of aromatase inhibitor therapy (anastrozole, exemestane, or letrozole) for adjuvant treatment of breast cancer or for chemoprevention up to 30 days following baseline visit (ok to initiate screening up to 2 months before planned baseline visit). Concurrent LHRH agonist, anti-HER2 directed therapy (e.g., trastuzumab, pertuzumab, ado-trastuzumab emtansine), and/or CDK4/6 inhibitor therapy (e.g., palbociclib, ribociclib, abemaciclib) is permitted. Prior tamoxifen and/or toremifene is permitted. * Completion of surgery (mastectomy or lumpectomy/partial mastectomy) for treatment of breast cancer. Completion of axillary surgery as indicated (not required). For patients at high risk of breast cancer who have not been diagnosed with breast cancer, no surgery is required. * Completion of chemotherapy, if indicated. Concurrent use of radiation therapy, LHRHa therapy, anti-HER2 therapy, PARP inhibitor, and CDK4/6 inhibitor therapy is permitted. Prior tamoxifen is permitted. * Agree to avoid taking omega-3 fatty acid supplements from sources outside the trial during study participation. * ECOG Performance Status ≤ 3. * Able to complete questionnaires in English. * Able to provide informed consent and willing to sign an approved consent form that conforms to federal and institutional guidelines. Exclusion Criteria * Prior use of AI therapy for treatment or prevention of breast cancer. * Use of omega-3 fatty acid supplementation during the 3 months prior to enrollment. Consumption of O3-FA through diet is permitted. * Use of warfarin, enoxaparin, or direct oral anticoagulants within 7 days prior to registration. * Known chronic liver disease (laboratory studies will not be assessed). Patients with hepatosteatosis, viral hepatitis, or other liver disorders who have adequate liver function according to the treating physician are permitted to enroll. * Known symptomatic paroxysmal atrial fibrillation or persistent atrial fibrillation (EKGs will not be performed). * History of pancreatitis. * Hypersensitivity to fish and/or shellfish. * Unable to take oral medications. * Any medical condition that would interfere with the absorption of study medication capsules. * Patients with a prior or concurrent malignancy whose natural history or treatment does not, in the opinion of the treating investigator, have the potential to interfere with the safety or efficacy assessment of the investigational regimen are eligible for this trial.