Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Breast Neoplasms Pre-Registration Diagnosis of pathologic stage II or III ER, PR, and HER2 negative primary invasive ductal or invasive lobular breast carcinoma. ER negative is defined as an Allred score of 0-2. PR negative is defined as an Allred score of 0-4. HER2 negative is defined as an IHC score of 0-1 and/or not-amplified by FISH testing All surgery for breast cancer (as defined by surgical excision of the cancer with a negative margin or mastectomy) must be complete Undergone axillary lymph node surgery (either sentinel lymph node biopsy or axillary lymph node dissection) per institutional standard Completed all (neo) adjuvant chemotherapy and radiation therapy as recommended by the treating physicians Completed the most recent cancer therapy (surgery, radiation, or chemotherapy) no less than 3 and no more than 24 weeks prior to registration. Note: patients who received experimental neoadjuvant or adjuvant therapy or surgical therapy (with the exception of Hh inhibitors) through participation in clinical trial are NOT excluded from this study as long as the other trial does not patients from enrolling into an additional adjuvant clinical trial and enrolling into this trial will not compromise the endpoints (primary and secondary) of the primary clinical trial. In addition, patients must have completed the experimental therapy no less than 4 weeks or 5 half lives (whichever is longer) and no more than 24 weeks prior to registration. For those patients who have enrolled into a neoadjuvant / adjuvant / surgical trial, all endpoints of these trials will be reviewed prior to consenting the patient for the sonidegib trial At least 18 years of age ECOG performance status ≤ 1 Patient (or legally authorized representative if applicable) must be able to understand and willing to sign an IRB approved written informed consent document. Pre-Registration  Concurrent treatment with any other standard therapy (e.g. chemotherapy, targeted therapy or radiotherapy) or within 3 weeks of starting sonidegib Treatment with investigational anti-cancer agent within 4 weeks or 5 half-lives whichever is longer, of initializing treatments with sonidegib Previous treatment with systemic sonidegib or with other Hh pathway inhibitors Diagnosis of a neuromuscular disorder (e.g., inflammatory myopathies, muscular dystrophy, amyotrophic lateral sclerosis, spinal muscular atrophy) or on concomitant treatment with drugs that are recognized to cause rhabdomyolysis (such as HMG CoA inhibitors (statins), clofibrate and gemfibrozil) and that cannot be discontinued at least 2 weeks prior to starting sonidegib treatment. If it is essential that the patient stays on a statin to control hyperlipidemia, only pravastatin may be used with extra caution Known to be HIV-positive on combination antiretroviral therapy because of the potential for pharmacokinetic interactions with sonidegib. In addition, these patients are at increased risk of lethal infections when treated with marrow-suppressive therapy. Appropriate studies will be undertaken in patients receiving combination antiretroviral therapy when indicated. Registration Presence of bone marrow DTCs after the completion of all intended breast cancer therapy including surgery, (neo) adjuvant chemotherapy therapy, and radiation as indicated. Note: Bone marrow aspiration will be performed in consented patients to evaluate DTCs provided patients meet all as described in this section ECOG performance status ≤ 1 Normal bone marrow and organ function as defined below Leukocytes ≥ 3,000/mcL Absolute neutrophil count ≥ 1,500/mcL