Breast Abscess: A localized collection of pus in the breast tissue, often presenting as a red, firm, and painful lump. This condition is commonly associated with lactational mastitis but can also occur in non-lactating women.

Inflammatory Breast Cancer (IBC): A rare and aggressive form of breast cancer characterized by rapid onset of inflammation and enlargement of the breast, often with a firm, red lump. It's crucial to differentiate IBC from other inflammatory conditions due to its poor prognosis if not promptly treated.
Fat Necrosis: A benign condition resulting from trauma to the breast, leading to the formation of firm, sometimes painful lumps. It can mimic breast cancer and may present with skin retraction or a red, firm lump.
Mastitis: An inflammation of the breast tissue, which can be infectious or non-infectious. It often presents with redness, swelling, and a firm, painful area of the breast.

Inflammatory Carcinoma: Although rare, this aggressive form of breast cancer can present similarly to mastitis or an abscess, with redness, swelling, and warmth of the breast skin. Missing this diagnosis could lead to delayed treatment and a poor outcome.
Necrotizing Fasciitis: A severe infection of the skin and subcutaneous tissue, which, although rare in the breast, can present with redness, swelling, and firmness. It requires immediate medical attention due to its high mortality rate.

Granulomatous Mastitis: A rare, chronic inflammatory condition of the breast, characterized by granulomatous inflammation. It can present with a firm, sometimes painful lump and may mimic breast cancer or other inflammatory conditions.
Sarcoidosis of the Breast: A rare condition where sarcoid granulomas form in the breast tissue, potentially causing lumps. It's part of a systemic disease that can affect multiple organs, including the lungs, skin, and eyes.