Aim: Reporting a patient with unusual metastatic site of invasive lobular breast cancer (ILC) as initial presentation of the disease. Introduction: Due to specific growth pattern, ILC rarely forms an apparent tumor, which makes diagnosis very challenging at early stage. ILC is also known for unconventional metastatic spread, with deposits being discovered prior to the primary tumor in 3-10% of cases. Case report: While evaluating renal function in 51-year old female patient hospitalised at the Urology Clinic (Clinical centre of Montenegro), static scintigraphy revealed left kidney functional capacity of 7-8%. Nephrectomy was indicated. Kidney, 11x6x4cm in size, with slightly reduced, paler parenchyma, firmly attached fatty capsule and pyelocaliceal system and ureter of regular gross appearence, was delivered to the Centre for Pathology. Analysis of H E sections revealed chronic pyelonephritis. In a few sections taken from urether, pyelon and subcapsular parts of parenchyma, infiltrates of small, cuboid, atipical cells, mostly arranged in one-cell-thick files, were noted. Immunohistochemistry reveiled strong pozitivity for EMA, CK(ae1/ae3), CK7, estrogen and mammaglobin, with Ki67<10%. A few cells were progesteron positive, while vimentin, CK20 and neuroendocrine markers were negative. ILC metastasis was suspected. ILC, with axillary lymph POSTER SESIJA 66 MATERIA MEDICA • Vol. 34 • Issue 1, suplement 1 • april 2018. node involvement, was confirmed later, although there was no macroscopically apparent tumor in the breast. Tumor cells were estrogen and progesterone positive, HER2 negative, with Ki67 of 3%. Conclusion: While assessing metastatic deposits in unconventional sites in women, primary ILC should be considered. Special diagnostic algorhytm is required for efficient initial detection of the primary tumor.

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