Metastatic invasive lobular carcinoma of the breast masquerading as a primary renal malignancy.

Breast cancer is known to metastasise to different organs in the body, but an initial presentation of breast cancer with loin pain secondary to a metastatic renal mass is extremely rare. We report a 58-year-old woman who presented with recurrent left loin pain due to a metastatic deposit of invasive lobular carcinoma of the breast. The detection of a renal mass on computed tomography led to the assumption of a renal pelvic malignancy. The diagnostic dilemma posed by the detection of a breast mass during staging and the usefulness of immunohistochemistry in the confirmation of diagnosis are discussed.