Context and objective: Despite extensive molecular investigation of adrenal pheochromocytomas, no information is available on their molecular and mismatch repair (MMR) profile by topographic compartments.

Design and setting: Microdissected samples from the peripheral and internal zones of 143 pheochromocytomas from a referral Hospital (95 sporadic, 48 associated to MEN-2A) were selected for loss of heterozygosity (LOH) and single nucleotide polymorphism (SNP) analyses. Five polymorphic DNA regions from TP53, RB1, WT1, and NF1 were systematically studied by PCR-denaturing gradient gel electrophoresis.

Patients, outcome measures, and interventions: Pheochromocytomas were classified malignant (16 sporadic tumors with distant metastases), locally invasive (30 sporadic tumors showing retroperitoneal infiltration only), and benign (all remaining tumors). Statistical differences were evaluated using Fisher's exact test. MMR was assessed by MLH1/MSH2 sequencing and immunostaining in PCC with 2 abnormal microsatellites. No interventions were done in this study

Results: LOH/SNP involved TP53 in 40/134 informative cases (29.9%), RB1 in 22/106 informative cases (20.8%), WT1 in 32/120 informative cases (26.7%), and NF1 in 32/80 informative cases (40.0%). More genetic abnormalities involving the peripheral compartment were revealed in 34 pheochromocytomas (23.8%): 12/16 malignant, 10/30 locally invasive, and 12/97 benign. Multiple and coexistent genetic abnormalities characterized malignant pheochromocytomas (P < 0.001), whereas locally invasive pheochromocytomas showed significantly higher incidence of NF1 alterations (P < 0.001). No mutations were identified in MLH1/MSH2 but MMR proteins significantly decreased in peripheral compartments.

Conclusions: Multiple microsatellite alterations and topographic intratumor heterogeneity characterize malignant pheochromocytomas, suggesting a multistep tumorigenesis through somatic topographic down-regulation of MMR proteins. Locally invasive pheochromocytomas reveal topographic heterogeneity and single locus microsatellite alterations, especially involving NF1.