The main aim of the study is to evaluate the incidence of post-operative diagnosis of PC and atypical parathyroid neoplasm in patients who underwent surgery for pHPT in different European centers using the EUROCRINE® database. Moreover, we aim to evaluate the peri-operative surgical characteristics, operation extent, postoperative morbidity, and outcomes in these patients category.

Parathyroid cancer (PC) is one of the rarest malignancies (0.005% of all tumours) and it represents less than 1% of all the causes of primary hyperparathyroidism (pHPT).

It is frequently a sporadic disease, but it can be part of hereditary syndromes (i.e. HPT- JT, MEN, MEN2A and FIHP).

Clinical and biochemical presentation is usually more severe comparing to other forms of primary hyperparathyroidism as it is often associated to very high serum-calcium and PTH levels and target organs' damages.

Malignancy should be suspected on the basis of the aforementioned biochemical data and the imaging evidences (such as parathyroid lesion dimension >3 cm, faded edges, inhomogeneous internal features and cervical lymph nodes enlargement).

In case of suspected PC a radical treatment should be proposed to the patient, consisting of parathyroidectomy and en bloc ipsilateral hemithyroidectomy and ipsilateral central neck dissection. Indeed, the oncological radicality during surgical treatment is mandatory, as effective adjuvant therapy is not available.

However, pre-operative differential diagnosis with parathyroid adenoma is still challenging, thus malignancy can be detected only after the histological analysis of the specimen and sometimes after recurrences.

Moreover, parathyroid atypical adenoma entity is still controversial, as it presents suspicious histological features, but certain signs of malignancy are lacking (such as capsular, vessels and neural invasion). Furthermore, natural history and biological behaviour are still unknown.

Inclusion Criteria: All adult (18 years old and older) patients that underwent surgery for primary hyperparathyroidism with a final histology of parathyroid carcinoma from 2015 till 2021.

Inclusion Criteria:

• All adult (18 years old and older) patients
• underwent surgery
• final histology of parathyroid carcinoma
• among European centers that participate in the Eurocrine® database between 2015 and 2021

Exclusion Criteria:

• Patients <18 years old

Patients with final histology of parathyroid carcinoma operated among European centers that participate in the Eurocrine® database between 2015 and 2021

Reasonable requests will be evaluated by the Eurocrine Council