Trauma or Contusion: This is the most likely diagnosis given the presence of a bruise, which typically results from blood leakage into the tissues following an injury. The lump could be a hematoma, which is a collection of blood outside of blood vessels, often caused by trauma.

Breast Cyst: A breast cyst is a fluid-filled sac within the breast. It can present as a lump and, if ruptured, could cause bruising.
Fibrocystic Changes: These are benign changes in the breast tissue that can cause lumps and, occasionally, bruising if there is significant inflammation or if a cyst ruptures.
Breast Abscess: An infection of the breast tissue that can cause a painful lump and, if severe, could lead to bruising due to inflammation and tissue damage.

Breast Cancer: Although less likely to present with bruising, breast cancer can cause a lump. It's crucial to rule out cancer, especially if the lump is new, growing, or accompanied by other symptoms like nipple discharge or skin changes.
Hematoma from a Biopsy or Surgical Procedure: If the patient has recently undergone a breast biopsy or surgery, a hematoma could form, causing a bruise and lump.

Fat Necrosis: A rare condition that occurs when fatty tissue in the breast dies, often due to injury. It can mimic cancer on imaging but typically presents with a lump and sometimes bruising.
Angiosarcoma of the Breast: A very rare and aggressive type of cancer that originates from the blood vessels of the breast. It can present with bruising and a lump, among other symptoms.
Hemangioma: A benign tumor made up of blood vessels. While rare in the breast, it could potentially cause a lump and, if ruptured, bruising.