We retrospectively studied clinical data of 96 patients diagnosed with local-regional recurrent PPGL in Peking Union Medical College Hospital, China. Local-regional recurrence referred to a reappearance of disease at the original site with or without metastases after complete surgical resection of the original tumor which had been confirmed by negative biochemical and imaging tests. Radiological features of local recurrence were often irregular in shape and closely adhered to surrounding tissues, and may be multiple nodules fused together. The recurrence-free survival was defined as the time elapsed from initial surgery until recurrence. Patients with metastases at onset, failure of complete resection of the primary tumor or new lesions which were not located at the original site of disease were excluded. We also retrospectively analyzed clinical data of 112 patients without recurrence with a median follow-up time of 8.0 (7.0, 9.8) years to study risk factors for recurrence. Patients without local-regional recurrence referred to those patients without recurrence or metastasis after complete resection of the primary tumor during the entire follow-up. Metastases were defined in accordance with the 2017 WHO classification of endocrine tumors. Metastases-free survival was defined as the time elapsed from initial surgery until metastasis. Clinical data, including gender, age at diagnosis, recurrence and metastases, symptoms, blood pressure (BP), primary tumor location, the maximum diameter of primary tumor, tumor secretion function (24-hour urinary catecholamine excretion), primary tumor pathology, genetic characteristics, treatment, and prognosis of recurrence were collected. The study was approved by the Institutional Review Board of Peking Union Medical College Hospital(S-K431). Written informed consent was obtained from all included patients.

All statistical analyses were conducted using Statistical Product and Service Solutions, version 21.0. Categorical data are presented as frequencies and percentages. Normally distributed data are expressed as mean ± standard deviation (x̄ ± s). Non-normally distributed data are presented as median and quartile range (25%, 75%). The association between two independent samples with a normal distribution was determined using independent sample T tests, while the association between two independent samples with a non-normal distribution was assessed using Wilcoxon rank sum tests. Associations between two dichotomous parameters were evaluated utilizing the Chi-square test. Kaplan-Meier testing was employed to describe progression-free recurrence. Factors validated in univariate analysis were further tested in multivariate analysis using Cox proportional hazard models. Results are reported as hazard ratios (HR) with 95% confidence intervals. All tests were conducted two-sided, with P values< 0.05 being considered statistically significant.

The 96 PPGL patients with local-regional recurrence included in this study, consisting of 67 PHEO patients and 29 PGL patients, exhibited an average diagnosis age of 32.2 ± 14.9 years, average recurrence age of 39.0 ± 15.4 years, and a median recurrence time of 6.0 (4.0, 9.0) years after resection of the primary tumor ( Figure 1 ). Twenty-one percent of patients (20/96) exhibited recurrence between 10 to 20 years after the initial surgery, and one patient exhibited recurrence 23 years after the initial surgery. Among recurrent patients, 47% (45/96) had multiple nodules in recurrent site, and 58% (56/96) had metastases, of which 71% (40/56) were synchronous metastases (recurrence accompanied with metastases) and 34% (19/56) were implantation metastases. At the current follow-up, seven recurrent patients had died. The 112 non-recurrent patients included 75 PHEO patients, 33 PGL patients and 4 patients with both PHEO and PGL. Non-recurrent patients had an average diagnosis age of 40.5 ± 12.9 years and a median follow-up of 8.0 (7.0, 9.8) years. Germline mutations were screened in 182 patients by using next-generation sequencing (including genes VHL, RET, NF1, SDHA, SDHB, SDHC, SDHD, SDHAF2, MAX, TMEM127, FH and KIF1B) (8), and Sanger sequencing. 33% (60/182) patients carried pathogenetic mutations in genes including SDHB, VHL, RET, MAX, SDHD and SDHA.

Compared with non-recurrent patients, recurrent patients exhibited at a younger diagnosis age (32.2 ± 14.9 in recurrent vs. 40.5 ± 12.9 in non-recurrent patients, p=0.000). Moreover, among the recurrent patients was a higher proportion of patients with primary tumor sizes ≥ 5cm (78% vs. 51% in non-recurrent patients, p=0.000), and a higher proportion of patients with gene mutations (42% vs. 26%, p=0.020), in particular in the SDHB gene (19% vs. 6% p=0.005). The proportion of patients with a primary tumor resection by laparotomy was higher than in the non-recurrent group (54% vs. 27% p=0.001) and the pathological features of the primary tumors of recurrent patients were more aggressive, manifesting more frequently as capsular invasion (20% vs. 5%, p=0.002), with vascular tumor emboli occurring more frequently (14% vs. 4%, p=0.018). Moreover, both the average Ki-67 count [4.5% (2%, 8%) vs. 1% (<1%, 2%), P=0.001] or the proportion of patients with an average Ki-67 count ≥ 3% (43% vs. 17%, p=0.001) were higher in recurrent than in non-recurrent patients. In contrast, there were no statistically significant differences in tumor functionality, levels of serum neuron specific enolase, primary tumor sites, proportion of patients presenting with typical symptoms, or RET/VHL/SDHD/SDHA/MAX mutation frequencies between the two groups ( Table 1 ).

SDHB mutation [HR 2.1 (1.2, 3.4), p=0.014], primary tumor size ≥5cm [HR 2.0 (1.2, 3.4), p=0.007], capsular invasion of the primary tumor [HR 2.0 (1.1, 3.7), p=0.016], and an average Ki-67 count ≥3% [HR 2.6 (1.5, 4.4), p=0.001] in the primary pathology were risk factors for recurrence in PPGL patients in univariable COX regression analysis ( Table 2 ). SDHB mutation [HR 4.1 (1.7, 9.5), p=0.001), a primary tumor size ≥5cm [HR 2.3 (1.1, 4.7), p=0.028], and average Ki-67 count ≥3% [HR 2.6 (1.4, 4.9), p=0.003] represented independent predictors for recurrence in multivariate analysis ( Table 2 and Figure 2 ).

The study included 146 PHEO patients, including 67 recurrent patients and 79 non-recurrent patients. Compared with non-recurrent PHEO patients, recurrent patients of PHEO presented at a younger diagnosis age (32.8 ± 15.3 in recurrent vs. 39.4 ± 13.3 in non-recurrent patients, p=0.007) and exhibited a larger primary tumor size (6.3 ± 2.3 vs. 5.5 ± 2.5 p=0.048). Among patients with recurrence there was a larger proportion of patients with a primary tumor size ≥5cm (75% vs. 46%). Both the average Ki-67 count [2% (1%, 5%) vs. 1% (1%, 2%), P=0.005] or the proportion of patients with an average Ki-67 count ≥3% (38% vs. 13%, p=0.002) were higher in recurrent patients ( Table 3 ). Primary tumor sizes ≥5cm [HR 5.1 (1.7,15.3), p=0.003] and an average Ki-67 count ≥3% of primary tumor [HR 2.4 (1.1, 5.2), p=0.035] were independent predictors for recurrence of PHEO in multivariate COX regression analysis ( Figure 3 ).

The study consisted of 66 PGL patients, including 29 recurrent patients (27 retroperitoneal PGL, 1 bladder PGL, and 1 cardiac PGL) and 37 non-recurrent patients (33 retroperitoneal PGL, 3 bladder PGL, and 1 cardiac PGL). Compared with the non-recurrent PGL patients, recurrent patients of PGL presented at a younger diagnosis age (30.7 ± 13.8 in recurrent patients vs. 43.7 ± 11.9 years in non-recurrent patients, p=0.000) and a higher proportion of patients with a SDHB mutation (40% vs. 9%, p=0.004). The primary tumors pathological characteristics of recurrent patients were more aggressive, manifesting more frequently as capsular invasion (29% vs. 6% in non-recurrent patients, p=0.023), vascular tumor emboli happened more frequently (17% vs. 0%, p=0.008), and both the average Ki-67 count [3% (1%, 4%) vs. 1% (1%, 3%), p=0.021] or the proportion of patients with an average Ki-67 count ≥ 3% was higher in recurrent patients (53% vs. 23%, p=0.049) ( Table 4 ). SDHB mutations [HR 4.6 (1.5, 13.9), p=0.007] were independent predictors for PGL recurrence in multivariate analysis ( Figure 4 ).

Among recurrent patients, 58% (56/96) had metastases. Most of these patients exhibited multi-system metastases, including 34% (19/56) implantation metastases, 34% (19/56) lung metastases, 30% (17/56) bone metastases, 27% (15/56) lymph node metastases, and 21% (12/56) liver metastases. SDHB mutations [HR 3.6 (1.3, 10.2), p=0.017] were an independent predictor for metastases by multivariate analysis ( Figure 5 ). The study included 19 patients with implantation metastases. These patients exhibited an average diagnosis age of 37.1 ± 15.3 years, an average recurrence age of 42.8 ± 15.5 years, and a median recurrence time of 5 (4, 7) years. The average primary tumor diameter was 6.1 ± 1.8 cm, and 89% (17/19) were PHEO, of which 37% (7/19) were left adrenal PHEO, 42% (8/19) were right adrenal PHEO, 10% (2/19) were bilateral adrenal PHEO. Ten percent of patient with implantation metastases (2/19) had distant metastases, with one patient exhibiting a liver metastasis and the other exhibiting bone and lymph node metastasis. No independent predictors for implantation metastases were found in multivariate analysis.

Thirty-two percent of recurrent patients (31/96) underwent surgery, of which 81% (25/31) patients underwent surgery only. However, 48% (12/25) exhibited recurrence after reoperation with a median time of recurrence of 3 (1.8, 4.2) years ( Figure 6 ). Recurrent lesions in 19% (6/25) of these recurrent patients had not been completely resected, and patients therefore received MIBG, radiotherapy, and chemotherapy, amongst other therapeutic options. Forty-three percent of recurrent patients (41/96) could not undergo surgery. Of these patients, 78% (32/41) patients received MIBG treatment, 12% (5/41) patients underwent chemotherapy/targeted therapy, and 10% (4/41) patients underwent radiotherapy. Fourteen percent of recurrent patients (13/96) were recommended for surgery, but refused and did not receive any other treatment. Of these patients, five developed metastases during the observation period, one patient could not undergo surgery during the observation peried as the lesion progressed and invaded surrounding organs, and 2 patients died of metastases. Compared with the treated patients, the risk of metastases and death was significantly increased in the untreated patients (42% vs. 25%, p=0.030, and 15% vs. 8%, p=0.003, respectively). The treatment records of the remaining 11% (11/96) recurrent patients were unclear due to lost to follow-up after the diagnosis of recurrence.