The clinical importance of parathyroid atypia: Is long-term surveillance necessary?

Abstract

The uncommon diagnosis of atypical parathyroid adenoma (APA) creates a clinical conundrum for surveillance. We evaluated a large series of APA to determine long-term outcomes. Prospectively collected data were retrieved for patients with a diagnosis of histologic APA defined by presence of ≥2 criteria: clinical/intraoperative adherence, fibrotic bands, trabecular growth, or mitotic rate of >1/10 per high-power field without indisputable signs of malignancy. Follow-up was at 2 weeks, 6 months, and yearly thereafter. From 1970 to 2014, 51 patients (1.2%) with primary hyperparathyroidism had a diagnosed APA. Mean age was 56 years (range, 19-83), and 61% were women. Intraoperatively, 11 of 51 glands (22%) were adherent, requiring concurrent thyroid lobectomy. Common microscopic findings were fibrosis (78%), trabecular growth (37%), and increased mitotic count (24%); the mean APA weight was 3.14 g (range, 167 mg-38 g). Loss of heterozygosity occurred in 25 of 38 tested patients (66%) at the p21 locus in 9 cases, at CDC73 and PTEN in 6, and at RB1 in 4 cases, with mean fractional allelic loss of 24% (range, 6-79). With mean follow-up of 5 years (range, 0.5-18), no patient has developed recurrence. Over a mean follow-up of 5 years, we observed no recurrences after APA resection. Molecular features had no discernable impact, indicating that long-term follow-up may be unnecessary.