Ruxolitinib for Premalignant Breast Disease

Inclusion Criteria: * Have a breast biopsy showing ADH (atypical ductal hyperplasia), ALH (atypical lobular hyperplasia), LCIS (lobular carcinoma in situ), or DCIS (ductal carcinoma in situ) requiring surgical excision. Microinvasive disease is allowed. * NOTE: Tissue from the diagnostic biopsy must be accessible/available for research correlates (i.e., a tissue block or \~10 unstained slides). Due to the nature of the study, fewer slides may be accepted with prior permission from the Protocol Chair if there is insufficient tissue. * Women and men age 18 and older. * Adequate hematologic and organ function, defined as follows: * Absolute neutrophil count ≥ 1500/mm3 * Hemoglobin ≥ 9.0 g/dL * Platelet levels \>200 x 109/L * Total bilirubin ≤ 1.5 x institutional upper limit of normal (ULN) * AST/ALT ≤ 2.5 x institutional ULN * Alkaline phosphatase ≤ 5 x institutional ULN * Creatinine clearance \> 50 mL/min as calculated by the Cockcroft-Gault method * Willing to not use concomitant strong CYP3A4 inhibitors as this could interfere with the metabolism of ruxolitinib (i.e azole antifungals, clarithromycin, conivaptan, grapefruit juice, mibefradil, nefazodone, protease inhibitors, telithromycin). * Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. * If the patient undergoes germline genetic testing, the results must be received prior to randomization, as the results may affect the surgical approach and, in turn, the date of surgical excision. * Patient understands the study regimen, its requirements, risks, and discomforts, and is able and willing to sign a written informed consent document. Exclusion Criteria: * Treatment with selective estrogen receptor modulators (SERMs) or aromatase inhibitors for breast cancer prevention within 1 year prior to starting study treatment. * Treatment with any other investigational agents within 30 days of starting study treatment. * Current diagnosis of invasive breast cancer (current microinvasive disease is allowed), or previous history of invasive breast cancer diagnosed within the last 5 years. NOTE: If previous history of ER+ invasive breast cancer diagnosed \> 5 years ago, patient must be off endocrine therapy for at least 1 year prior to starting study treatment. * Uncontrolled intercurrent illness including, but not limited to ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, end stage renal disease (ESRD), or psychiatric illness/social situations that would limit compliance with study requirements. * Women who are pregnant or nursing. * HIV-positive participants on combination antiretroviral therapy are ineligible because of the potential for pharmacokinetic interactions with ruxolitinib. * Prior or current treatment with a JAK inhibitor, for any indication. * Known active Hepatitis B or C.