Morphological Harbingers of ARMC5-Pathogenic Variant-Related Bilateral Macronodular Adrenocortical Disease

Bilateral macronodular adrenocortical disease (BMAD) is a neoplastic disease associated with a high frequency of germline disease. Armadillo repeat containing 5 (ARMC5) pathogenic variants (PVs) have not been widely studied to determine the morphological and immunohistochemical characteristics of BMAD. We carried out a detailed morphologic review of 22 surgical specimens excised from patients with BMAD and compared them with PV of ARMC5 (PV + , n = 14) and those without (PV - , n = 8), and further comparing them with a control group of adrenals excised from patients with renal cancer (n = 11). No patients presented with a genetic syndrome related to BMAD. Overt Cushing's syndrome was present in 12/22 patients, 10 PV + and 2 PV - (p = 0.074). We also evaluated the expression of Ki-67, BCL-2, BAX, p53, CYP11B1, and ARMC5 protein. The pseudo-glandular and trabecular architectural patterns were strongly associated with the PV + group (both p < 0.001), as well as capsular extrusion (p < 0.001). There was no predictive value in the distinction of ARMC5 variants in Hsiao subtyping. ARMC5 diffuse cytoplasmic staining was observed in all 11 control samples. The ARMC5 expression was significantly lower in BMAD than in the control group (p < 0.001). In all the specimens, expression of BCL-2 was identified only in the medulla, and expression of BAX was observed in adrenocortical cells. CYP11B1 diffuse immunoexpression was identified in all the specimens of BMAD and in the fasciculata zone in the control group. The mitotic count and Ki-67 proliferation index was very low in all three groups (controls, PV + , and PV - BMAD). None of the specimens stained positive for the p53 protein. Although our series is limited, the presence of pseudo-glandular and/or trabecular patterns and capsular extrusion indicated the presence of pathogenic variants of ARMC5 in BMAD. The gland enlargement does not seem to be related to the increase of mitotic count or a higher proliferation index (Ki-67).