PLEOMORPHIC HYALINIZING ANGIOECTATIC TUMOR (PHAT) OF RENAL PARENCHYMA. FIRST CASE REPORTED IN LITERATURE

Introduction: The pleomorphic hyalinizing angiectatic tumor(PHAT) is a rare non-metastatic tumor of soft tissueidentified in 1996 (1). In adults, it generally occurs in thesubcutaneous tissue of the lower limbs, although reportedalso in chest wall, buttock and arms. In the literature, onlyone case of PHAT has been described in the kidney at thelevel of the hilum but not involving renal pelvis orparenchyma (2). The clinical behavior of PHAT ischaracterized by a slow growth and a rate of localrecurrences higher than 50%. Metastasis has not beenreported. Case Report: A 61-year-old Caucasian obesefemale with a medical history of hypertension andhypercholesterolemia was admitted at the Emergency Unitfor recurring gross hematuria since one year, becoming morefrequent and severe in the last 3 months. Due to the severeanemia (hemoglobin of 7.7g/dl), the patient was transfused.Computed tomography (CT) scan revealed a parenchymallesion of 4 cm in diameter of the lower pole of the rightkidney. The lesion was only partially capsulated, mixed witha well evident cystic component, in strict contact with thelower calyx suspicious for infiltration. At cystoscopy, a clotemerging from the right ureteral meatus was evident. Urinecytology was negative and no imaging was indicative oftransitional upper urinary tract tumor. After written informedconsent, a right nephrectomy was performed and the patientwas discharged on the 4th day. The histological examrevealed a partially capsulated lesion (3.7 cm in diameter)with a pseudo-cystic structure, including hemosiderindepositions, compressing but not invading the dilated lowercalyx. The lesion was characterized by hyalinized clusters ofthin-walled ectatic blood vessels within a stroma composedof sheets and fascicles of spindled and pleomorphic atypical cells with intranuclear inclusions. At immunohistochemicalanalysis, AE1/AE3, EMA, CD31, S100, desmin, actin ofsmooth muscle, HMB45, ALK resulted negative. The lesionwas classified as a PHAT. The patient is maintained infollow-up. Discussion: PHAT is a low-grade mesenchymalneoplasm of uncertain lineage described in soft tissue andcharacterized by diffusely infiltrative borders, although somedo have well-circumscribed margins. The immunohistostainingfor S-100 protein, actin, desmin, cytokeratin,CD-31, factor VIII antigens or epithelial membrane antigenare negative. To date approximately 22 cases of PHAT and40 cases of its precursor, "early PHAT", have been describedin the world literature. At least 3 cases of PHAT werereported to progress to high-grade myxofibrosarcoma (1). Acase of PHAT arising in the hilum of the kidney, clinicallymimicking an infiltrating tumor of the renal pelvis, has beendescribed in 2012 (2). Our case is the second described inretro-peritoneum and the first of the renal parenchyma. In ourpatient, a partial nephrectomy was not carried out due to theabsence of well-defined margins and apparent involvement ofthe lower calyx, although not confirmed by the pathologicalexam. If a partial nephrectomy is performed, a strict followupshould be considered due to the high percentage of localrecurrence characterizing the clinical behavior of PHAT (3).1 Shi Wei et al: Complex analysis of a recurrent pleomorphichyalinizing angiectatic tumor of soft parts. HumanPathology 43: 121-126, 2012.2 Muhammad T et al: Pleomorphic hyalinizing angiectatictumor of renal hilum. Annals of Diagnostic Pathology 16:489-493, 2012.3 Folpe AL and Weiss SW: Pleomorphic hyalinizingangiectatic tumor: analysis of 41 cases supportingevolution from a distinctive precursor lesion. Am J