The patient indicates the pain increases with movement especially external rotation and abduction. She feels worse at night as the pain wakes her up. The pain, stiffness and loss of motion have been gradual and she denies any acute trauma. This patient has a history of breast cancer. She had a bilateral mastectomy and has had recent surgery for metastasis to her left lung for which a portion of her lower left lobe was removed. This patient is on hormone reduction therapy for her breast cancer. She is retired. She is on no medications and is an active dancer.

Question: Based on this clinical history, what are some of the differential diagnoses you are considering?