[Clinicopathological characteristics of fumarate hydratase-deficient renal cell carcinoma]

Objective: To investigate the clinicopathologic characteristics, molecular and genetic features, differential diagnoses and prognosis of fumarate hydratase-deficient renal cell carcinoma (FH-RCC). Methods: The immunohistochemical (IHC) expression of FH in 391 renal neoplasms in tissue chips collected from the Affiliated Hospital of Qingdao University and 971 Hospital of PLA Navy from January 2011 to December 2017 was evaluated. The clinicopathologic data of eight FH negative cases were collected.Polymerase chain reaction (PCR) and sequencing were used to detect the changes in FH gene in three cases. Interphase FISH with a dual color and break-apart probe was applied to detect the TFE3 gene alteration in the cases showing TFE3 protein expression. Results: Among the eight patients, seven were male and one was female, and age ranged from 28 to 50 years (mean 39 years). Tumor size ranged from 3.5 cm to 12.0 cm (mean 7.9 cm). Renal pelvis invasion was identified in six cases, and the tumor emboli in renal vein and inferior vena cava were found in four patients. The cut surface of most tumors was solid, colorful, grayish white or yellow with no clear border showing invasive growth pattern. Microscopically, the tumors showed different proportions of papillary, tubular cystic, cribriform and solid structures. The tumor cells were rounded or polygonal with eosinophilic or amphotropic cytoplasm, round or oval nuclei, and focal large and prominent nucleoli (WHO/ISUP grade 3-4). Two cases had sarcomatoid or rhabdoid components. Intravascular tumor emboli were found in five cases. IHC staining showed most tumors expressed PAX8(7/8), CK19(7/8), vimentin (6/8) and P504s(8/8). However, other immunomarkers including CK7, CD10, CD117, RCC, 34βE12, HMB45 and Melan A were all negative. Sequencing showed all three cases had FH gene mutations in exon 1. FISH revealed no TFE3 gene translocation or amplification in the two cases with TFE3 IHC expression. Follow-up data were available in seven patients with the follow-up period from 11 to 66 months. Among them, five patients died between 11 to 31 months after the surgery because of extensive distant metastases of the tumor to the lung, liver and lymph nodes. The other two patients were alive at the 36th and 66th month after the surgery. Conclusions: Morphologically, FH-RCC overlaps with papillary RCC, collecting duct carcinoma and tubular-cystic RCC, showing a mixture of papillary, tubular cystic, cribriform or tubular papillary structures with at least focal large and prominent nucleoli. The negative expression of FH and the detection of FH gene mutation could facilitate the diagnosis of the tumor. FH-RCC is a high aggressive tumor, prone to metastasize, and is associated with poor prognosis. The timely diagnosis of FH-RCC could benefit the patients and their relatives as well.