3.3 Survival analysis
There was no operative mortality in this cohort. Four patients died within 1 month after adrenalectomy (on day 5, 16, 22 and 30, respectively) as a result of multiple organ dysfunction syndrome and progression of NEN. At the end of the follow-up period, 14 patients were still alive and 39 had died.
Median survival after BA was 24 months (95% confidence interval [CI] = 7–41, min-max: 0–428) with a 5-year survival of 22%. Median follow-up time for all patients from time of ECS diagnosis was 26 (range 6–62) months and after BA was 19 (range 3–50) months. OS was longer in patients where ECS was treated by radical surgery of the primary tumour or where good biochemical control was achieved by SI compared to patients who underwent BA, 96 months (95% CI 0–206) vs 29 months (95% CI 7–51), respectively. However, this difference was not statistically significant (p = .086), most likely as a result of the small sample size. Multiple hormone secretion correlated with shorter OS after BA (p = .009; hazard ratio = 2.9; 95% CI= 1.3–6.7). There was no significant difference in OS after BA depending on localisation of primary tumour (thoracic NENs 24 months [95% CI = 8–40, min-max: 0–428], pancreatic NENs 19 months [95% CI = 0–43, min-max: 0–60], p = .319) or surgical approach (open access approach 24 months [95% CI = 1–47], endoscopic approach 19 months [95% CI = 1–37], p = .720).
Median time from ECS diagnosis to BA was 2 months (range 1–10). Patients who underwent BA within 2 months after ECS diagnosis had shorter OS compared to those who were operated at a later stage: 6 months (95% CI = 0–18) and 45 months (95% CI = 3–86) respectively (p = .007). The former group had a slightly higher median Ki-67 level (18% vs 9%), lower potassium (2.7 mmol L-1 vs 3.0 mmol L-1) and higher hormone levels (ACTH 217 vs 120 ng mL-1, morning cortisol 1448 vs 1181 nmol L-1 and UFC 5716 vs 4234 nmol per 24 h) at diagnosis compared to those who were operated later in the course of disease.
4 DISCUSSION
The present study highlights new aspects of the advantages of an endoscopic approach of BA compared to open access surgery, regarding the incidence of severe complications graded using the Clavien-Dindo classification, as well as operation- and hospitalisation time. Our results indicate that PRA performed by two surgeons simultaneously is the method of choice for patients with ECS. However, despite these advantages, the endoscopic approach did not appear to improve overall survival.
Recent Endocrine Society guidelines recommend SI as primary treatment for ECS in patients with occult or metastatic ECS followed by BA.6 Although the toxicity of SI in our cohort was low (n = 2; 6%), 32 patients (73%) had persistent hypercortisolaemia despite medical treatment and proceeded to BA. BA, especially with an endoscopic approach, with a short operating time and low complication risk, appears to play a major role in the appropriate management of hypercortisolaemia in ECS, where rapid reduction of cortisol levels is very important.
Prolonged exposure to high cortisol levels, in combination with high risk for hepatotoxic and nephrotoxic SI side effects, increases morbidity and risk for severe complications, and often delays the start of oncological treatment. However, the trauma caused by surgery can also postpone initiation of chemotherapy.21 Therefore, a fast and minimally invasive surgical procedure appears to be a crucial factor for the better survival in ECS. The endoscopic approach is now considered as the gold standard for BA. Our study presents fewer severe complications, as well as shorter operating and hospitalisation times, when the endoscopic approach is compared with open surgery. In line with previous studies,19, 22 we observed a significantly shorter operating time when applying PRA compared to LTA because there is no need for repositioning of the patient during PRA. PRA-2S had the shortest operating time and should be considered as the best choice of surgical approach in ECS. This result ties well with previous studies reporting the median operating time to be between 43 and 157 min in PRA-2S, which is significantly shorter compared to LTA and PRA-1S.17–19
The median time from diagnosis to BA was 2 months, which is consistent with a previous study.23 However, OS was significantly shorter in patients who were operated within 2 months after diagnosis of ECS in our cohort compared to those operated at a later stage. These early operated patients probably had a more aggressive clinical course of disease, as indicated by slightly higher median Ki-67, lower potassium and higher hormone levels at diagnosis, and they were operated as a result of more acute indications (without time to proper pre-treatment with SI) than the other group.
In our previous report on patients with ACTH-producing NENs, multiple hormone secretion was identified as the strongest indicator of a worse prognosis.4 A similar pattern of results was observed in this cohort, showing that patients with NENs, with concomitant hypersecretion of other hormones than ACTH from their tumour, had a shorter OS after BA compared to those with ACTH hypersecretion only.
As a result of the extremely high preoperative cortisol levels in ECS, the substitution therapy needed after successful BA may be challenging.21 Over-replacement of glucocorticoids may lead to higher morbidity24 and mortality, especially in patients with metastatic NENs, who often have impaired immune function because of oncological treatment. Many patients suffer from glucocorticoid withdrawal syndrome, despite adequate replacement therapy, and it can take ≥ 1 year to gain control over these symptoms.6 This frequently leads to high dosage of glucocorticoids. The Endocrine Society guidelines recommend glucocorticoid replacement with hydrocortisone, 10–12 mg m-2 day-1 in divided doses.6 If we assume that most of our patients have body surface area around 2 m2 or less, the daily hydrocortisone dose should not exceed 25 mg. However, 1 year after BA, only one patient received 25 mg of hydrocortisone daily, with the majority receiving 30 mg or more. One-third of the patients had residual arterial hypertension and diabetes 3 months after BA, probably partially depending on too high a dose of glucocorticoids.
There was a higher complication rate in our cohort compared to other studies19, 25, 26 and five patients needed conversion from an endoscopic approach to open surgery. In particular, the outcome of BA in ECS has not previously been systematically evaluated27 because most of the reports include patients with various aetiologies of CS.19, 22, 23, 28, 29 In a systematic review of the literature published between 1980 and 2012 on BA in CS, Reincke et al23 identified 37 studies and ECS was present in 13% of the patients. There are only few papers focused on BA in ECS solely21, 25, 26, 30, 31 and only one has a cohort with > 50 patients (n = 54).26 Patients with ECS have almost always a more aggressive course and more severe metabolic disturbance than patients with other types of Cushing’s syndrome, which probably leads to higher risk for postoperative complications. Furthermore, multiple liver metastases, fibrotic processes in the abdomen as a result of previous surgery or large primary tumour in pancreas could be some of the factors influencing surgical outcome in ECS.
The present study has several limitations. First, all data were collected retrospectively from patient records and not all the preferred parameters were available for all patients. Second, even if our cohort is one of the largest regarding studies on BA in ECS, the number of patients is too low for reliable statistical analysis. Finally, our study covered more than three decades, BAs were performed at different clinics and by different surgeons. Therefore, the data should be interpreted carefully.
In conclusion, the present study is one of few reports focusing on BA in specifically NEN patients with ECS and includes one of the largest patient cohorts analysed in the field. PRA-2S can be considered as method of choice in ECS compared to other BA approaches. The aim is to avoid administrating too high a hydrocortisone replacement dosage postoperatively because this can worsen the metabolic disturbance. As a result of the rarity of the condition, multicentre studies are needed with large, prospective cohorts and standardised inclusion criteria, aiming to further improve our knowledge about the management of ECS.
ACKNOWLEDGEMENTS
This study was funded by the Swedish Cancer Society (grant number CAN 18 0576), the Lions Foundation for Cancer Research at Uppsala University Hospital, Selanders Foundation and Söderbergs foundation at Uppsala University.
CONFLICT OF INTERESTS
The authors declare that they have no conflicts of interest.
AUTHOR CONTRIBUTIONS
Ieva Lase: Conceptualisation; Data curation; Formal analysis; Investigation; Methodology; Visualisation; Writing – original draft; Writing – review & editing. Malin Grönberg: Formal analysis; Supervision; Visualisation; Writing – review & editing. Olov Norlén: Conceptualisation; Writing – review & editing. Peter Stålberg: Conceptualisation; Writing – review & editing. Staffan Welin: Conceptualisation; Supervision; Writing – review & editing. Eva Tiensuu Janson: Conceptualisation; Funding acquisition; Methodology; Supervision; Writing – review & editing.
ETHICAL APPROVAL
The need for informed consent was waived by the local ethics committee. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The study was approved by the local ethics committee, Regionala etikprövningsnämnden (EPN), in Uppsala, Sweden.