Perivascular Epithelioid Cell Tumor: A Clinicopathologic Study And Molecular Pathologic Analysis

Perivascular epithelioid cell tumor:a clinicopathologic study and molecular pathologic analysis Cai Junna Directed by Professor Wang Jian PurposeTo study the clinicopathologic characteristics, imaging findings and immunophenotype of perivascular epithelioid cell tumor (PEComa) with a purpose of exploring the value of the molecular genetics in the treament of this tumor especially in malignancy. Methods1.54 cases of PEComa were retrieved from the files of the Department of Pathology, Cancer Hospital, Fudan University between January 2004 and December 2010 and all the histological slides were reviewed for confirmation of pathologic diagnosis by a professional pathologist. The features of clinicopathologic, imaging findings and immunophenotype were analyzed and patient follow-up were continued.13 normal tissues were collected as a control group.2. HMB45, A103, PNL2, S-100, desmin, MiTF,α-SMA, MSA, vimentin, EMA and Ki67 proteins were immunohistochemically detected in cases using formalin-fixed, paraffin-embedded tissues by EnVision+two steps. The p-mTOR, p-AKT, p-S6 protein were the markers of mTOR pathway.3. Multiplex ligation-dependent probe amplification (MLPA) was performed to detect the abnormality of the TSC1, TSC2 gene in 25 cases. The normal tissues were collected as a control group. Fragment analysis was performed to investigate the role of the TSC1, TSC2 gene in cytogenetic process of PEComa, as well as the relationship with the activation of mTOR pathway.Results1. Clinical characters:(1) Gender:There were 17 male patients and 37 female patients (male to female,1:2.2) in 54 patients.(2) Age:The age of the patients ranged from 10 to 67 years with the median age of 43.0 years (average 41.6 years).61.6 percent of patients were aged 20～50 years.(3) Position:Perivascular epithelioid cell tumor-not otherwise specified (PEComa-NOS) occurred in abdominal/peritoneal cavity (n=13,24.1%), female genital tract (n=11, 23.1%) and gastrointestinal tract (n=4,9.6%). Other sites included thigh (n=2), mediastinum, left inguinal region, bladder and femur (one case each).14 PEComa cases occurred in kidney (21.2%,14/54). Two EAML cases occurred in liver and post-peritoneum (3.7%), one malignant CCST in lung (1.9%) and 3 LAM cases in abdominal cavity and mediastinum.(4) Clinical manifestations:The abdominal/peritoneal cavity patients always presented with masses, which were discovered incidentally or by physical examination, the others may manifested with pain, discomfort after eating, hematuria or waist soreness. The tumor involvement with uterus was discovered with abnormal menstrual cycle or hypogastralgia. Subcutaneous painless masses were presented in inguinal region and thigh. None of the cases was associated with tuberous sclerosis complex (TSC) or malignant melenoma.(5) Imaging examination:The type-B ultrasonic showed the hypoechoic and heterogeneous mass with abundant blood. CT and MRI examination showed the heterogeneous mass with low signal intensity; abundant vascular image may be recognized. Most PEComas cannot be reliably diagnosed on imaging studies before surgery.(6) Treatment:50 patients were treated with tumor resection,3 cases were performed with an exploratory laparotomy,1 case was just treated with chemotherapy.9 cases had chemo-therapy after surgery with no obvious therapeutic effect.5 cases also had radiotherapy in pelvic cavity area.3 cases had traditional Chinese medicine after surgery. One case was performed with palliative surgery.2 cases were treated with radiotherapy after explo-ratory laparotomy and 1 case had tgamma ray in the treatment. One case with tumor in right upper mediastinum could not be performed with a tumor resection and was treated with chemotherapy.37 patients didn't have any aftertreatment.(7) Prognosis:The course of the patients ranged from 3 to 54 months in 36 cases with follow-up data. A follow-up data of 25 in 30 patients with malignant PEComa showed that 12 cases were alive without diseases,9 cases alive with diseases and 4 cases died of the tumor.7 cases had recurrence, in which 5 cases had metastases.1 of 3 patients with PEComa of uncertain malignant potential (PEComa-UMP) were died after 27 months with chemotherapy,2 cases were alive without diseases.3 patients with benign PEComa were alive without diseases.4 AML patients and 1 EAML patients with follow-up data were alive without diseases.2. Pathologic findings:(1) General patterns:The size of tumors in different cases were various from 2cm to 40cm in diameter (average,9.2 cm). The masses were firm and the cut surfaces were offwhite to tan in color. Hemorrhage, necrosis or cystoid was seen in part of the cases. The cut surfaces of renal AML were always polychrome because of hemorrhage and adipose tissue, with areas of necrosis. The masses of LAM may be tan to gray in color. Pulmonary CCSTs are solitary and peripherally located tumor, the cut surfaces were translucent.(2) Histological findings:PEComa-NOS generally could be segregated into 3 morphologic groups, the first closely resembling CCST or epithelioid AML, were composed of clear to lightly eosinophilic cells. The second closely resembling CCMMT, with relatively uniform, moderate-sized spindled cells arranged in fascicles and nests arranged around an elaborate capillary network. The third were hybrid of epithelioid PEC and spindled PEC. The tumor cells grew in a fascicular, nested, and occasionally sheet-like pattern, and often were arranged in a radial fashion around blood vessels. Unusual features, seen in a significant minority of tumors, include multinucleated giant cells and "spider cell-like" cells, stromal hyalinization, and scattered markedly melanin pigmentation. Histologically malignant PEComas showed some combination of high nuclear grade, high cellularity, mitotic figures, coagulative tumor cell necrosis, and angiolymphatic space invasion. According to the criteria proposed by Folpe et al,20 cases (66.7%) were classified as malignant PEComa,5 cases (23.3%) as PEComa of uncertain malignant potential (PEComa-UMP) and 5 cases (23.3%) as benign.3. Immunohistochemical findings:The immunoreactivity of HMB45, PNL2 in tested cases was 100%, but varied from focal to diffuse area in different cases. The results of other markers were Melan-A (11/23,47.8%),α-SMA (20/32,62.5%), desmin (16/28, 57.1%), vimentin (18/24,75%), S-100 (3/18,14.3%), CD10 (4/16,25%), CD117 (4/15, 26.7%).4. Molecular genetics:(1) The result of immunohistochemistry showed the expression of three markers in the mTOR pathway. The expression of S6 was high in tumor tissue, accounting for 88% (22/25). The AKT protein was detected in normal tissue (61.5%,8/13). The expression of AKT was low in tumor tissue, only weak positive in one case. The expression of AKT and S6 protein in tumor tissue had a negative correlation (P<0.05). The expression of AKT protein in tumor tissue and normal tissue had a significant difference (P=0.000), so did S6 protein (P=0.028). The S6 protein was detect with a local and weak positivity in normal tissue, but with a strong and diffuse positivity in tumor tissue. There was a significant difference in degree and extent of expression (P =0.031). The immunoreactivity of mTOR was low in both tumor tissue and normal tissue, and no significant difference was found in two kinds of tissues (P=0.090).(2) The results of MLPA:Except for one case with low quality of DNA, the deletion and duplication of TSC1 gene were detected in 14 cases (58.3%,14/24), TSC2 gene detected in 16 cases (66.7%,16/24). Activation of mTOR pathway was concurrent with mutation of TSC1/2, the coincidence was 83.3%. Conclusions1. PEComa is a rare soft tissue tumor mainly occurs in young and middle-aged adults with a female predilection.2. The most common sites of PEComa-NOS were abdominal/peritoneal cavity and female genital tract, followed by gastrointestinal tract and urinary tract.3. Histologically, the perivascular epithelioid cell family of tumors was characterized by composing of PEC. The perivascular epithelioid cell could be spindled or epithelioid, the proportion varied from one case to another. PEComa-NOS could be segregated into CCST-like, CCMMT-like and a mixture of epithelioid and spindled cells. Abundant delicate vasculature could be seen in most of tumor.4. The immunophenotypic feature of PEComas was coexpressing the melanocytic and smooth muscle markers, the so-called myomelanocytic nature. Expression of two groups' markers is not always consistent in various sites of tumors. The tumors composed of mainly epithelioid cells major in expressing HMB45.α-SMA showed more positivity in spindle cells than epithelioid cells.5. The results of immunohistochemistry showed the activation of mTOR pathway, indicating that mTOR pathway had a role in development of PEComa. This suggests the possibility that mTOR inhibitors such as rapamycin may be therapeutic for this tumor especially for malignancy.6. The analysis of MLPA showed the frequent deletion or duplication of 16p13 in which TSC2 gene is located and 9q34 in which TSC1 gene is located. This indicates the oncogenetic relationship of PEComas as a TSC-linked neoplasm. TSC gene plays an important role in mTOR signaling pathway.