PHPT was the most frequent manifestation in both groups (80% of phenocopies vs. 81% of MEN1), but tumor associations differed significantly between groups (p < 0.001): 41% of MEN1 patients showed the classic triad, compared to only 1% of phenocopies; PHPT with NETs was more common in MEN1 (32%), whereas PHPT with PitNETs occurred more often in phenocopies (54%), reflecting patterns of sporadic tumors. The gene discussed is MEN1; the disease is neoplasm.