Lack of association between microsatellite instability and benign adrenal tumors

Initial characterization of immune microenvironment in pheochromocytoma and paraganglioma

Due to fewer adverse events, faster onset of action, and longer durable responses compared to chemotherapy, immunotherapy has been widely used to treat advanced solid tumors. Moreover, immunotherapy can improve the autoimmune status, thus allowing patients to benefit from the treatment in the long term. The immune microenvironment status is closely associated with the response to chemotherapies. Here, we analyzed the characteristics of the immune microenvironment in pheochromocytoma and paraganglioma (PPGL). Immunohistochemistry showed that PD-L1 is sparely expressed in PPGL with low positive rates and low expression levels, an expression pattern, that is, not correlated with tumor malignancy. Moreover, the level of intratumoral CD4⁺ and CD8⁺ lymphocyte infiltration in PPGL is low, suggesting that the immune microenvironment in PPGL may be in "immune desertification" or "immune rejection" states in which CD4⁺ and CD8⁺ lymphocyte infiltration is prevented, rendering immunotherapy less effective. In sum, our results indicate that PPGL is a microsatellite-stable tumor with low tumor mutational burden (TMB) levels, weak neoantigen production, and poor tumor antigenicity, hinting at a poor response of PPGL to chemotherapies.

Large proportion of low frequency microsatellite-instability and loss of heterozygosity in pheochromocytoma and endocrine tumors detected with an extended marker panel

PURPOSE

Pheochromocytoma (PCC) is a usually benign tumor originated in the majority of patients from the adrenal medulla. Regarding sporadic forms of PCC, mechanisms of pathogenesis are largely unknown. Recently, microsatellite-instability (MSI) was discussed as genetic factor contributing to PCC development. Since microsatellite markers used for MSI detection have only been recommended for colorectal carcinoma (CRC), we established an extended marker set for MSI detection in PCC.

METHODS

Twenty-two PCC patients were analyzed applying 11 microsatellite markers. Our marker set comprised the reference panel for CRC and six additional markers, which have already been described to detect MSI in tumors other than CRC. Moreover, 23 endocrine tumors with gastrointestinal origin were examined in order to test the applicability of this marker panel.

RESULTS

Microsatellite-instability was detected in 41% of PCCs. Twenty-seven percent showed loss of heterozygosity (LOH) events affecting different chromosomal regions. Among the 23 patients with endocrine tumors, only three (one pancreatic endocrine tumor, one duodenal neuro-endocrine tumor, one hepatic metastasis of a primary tumor with unknown origin) demonstrated MSI.

CONCLUSIONS

The extended microsatellite panel is qualified to detect MSI in PCC. Nine percent of MSI-positive cases would have not been noticed by the use of the reference panel alone. PCCs are characterized by low frequency MSI pointing to failures in factors involved in DNA replication.