Clinical Utilization of CYP17A1 and CYP11B2 in Evaluating Cortisol- and Aldosterone-Producing Adrenal Nodules.

Mild autonomous cortisol secretion (MACS) has been increasingly recognized as a risk factor for cardiometabolic comorbidities and increased mortality. While CYP11B2 immunohistochemistry (IHC) based HISTALDO classification is well established for evaluating primary aldosteronism (PA), the clinical utility of CYP17A1 IHC in assessing cortisol- and aldosterone-producing adrenal nodules remains underexplored. We investigated the clinical utility of CYP17A1 IHC, in combination with mHISTALDO patterns, to distinguish cortisol-producing adrenal lesions across a spectrum of adrenal pathologies, focusing on patients with MACS only, PA only, and PA+MACS. As expected, normal adrenal cortex demonstrated diffuse, strong (3+) CYP17A1 expression in the zona fasciculata and zona reticularis, whereas markedly reduced CYP17A1 was seen in secondary adrenal atrophy. Non-functional adenomas showed patchy, weak CYP17A1 expression, while functioning adrenocortical carcinomas demonstrated marked intratumoral heterogeneity with loss of zonation. MACS adenomas showed diffuse (≥90%) CYP17A1 labeling, predominantly of strong intensity, though not exceeding that of the background cortex. Non-classical mHISTALDO patterns were identified in all PA+MACS patients, in which the adenomas were CYP17A1-positive and CYP11B2-negative. No overlapping labeling of CYP17A1 and CYP11B2 was observed in MACS and PA+MACS. In contrast, classical mHISTALDO patterns were present in all PA-only patients, with variable colocalization of CYP17A1 positivity in all CYP11B2-positive adenomas, without autonomous cortisol secretion. The colocalization ranged from small focal to diffuse, with weak to strong CYP17A1 intensity. The lack of hypercortisolism in PA-only patients argued against the cortisol-producing action of CYP17A1 in classical mHISTALDO. In summary, diffuse CYP17A1 expression was associated with adrenal nodules in MACS and in PA+MACS with non-classical patterns, and may provide supportive histologic evidence for lesions associated with cortisol co-secretion. In patients with classical patterns, CYP17A1 positivity in CYP11B2-positive adenomas may be misleading and should not be interpreted as evidence of cortisol overproduction. The combined use of CYP17A1 IHC and the mHISTALDO classification in PA patients may provide a diagnostic adjunct for identifying lesions with potential hormone co-secretion; however, clinical and biochemical correlation is essential in determining functional impact. In patients with PA, a non-classical mHISTALDO pattern and a CYP17A1-positive, CYP11B2-negative nodule may warrant additional evaluation for cortisol co-secretion and consideration of postoperative adrenal insufficiency. Our findings are preliminary, hypothesis-generating, and require validation in larger, independent cohorts.