Risk factors for complications after surgery for pancreatic neuroendocrine tumors.

BACKGROUND: Surgical resection is the only potentially curative treatment for pancreatic neuroendocrine tumors. The choice for the type of procedure is influenced by the expected oncological benefit and the anticipated risk of procedure-specific complications. Few studies have focused on complications in these patients. This cohort study aimed to assess complications and risk factors after resections of pancreatic neuroendocrine tumors. METHODS: Patients undergoing resection of a pancreatic neuroendocrine tumor were identified within 2 centers of excellence. Complications were assessed according to the Clavien-Dindo classification and the comprehensive complication index. Logistic regression was performed to compare surgical procedures with adjustment for potential confounders (Clavien-Dindo ≥3). RESULTS: The cohort comprised 123 patients, including 12 enucleations, 50 distal pancreatectomies, 51 pancreatoduodenectomies, and 10 total/combined pancreatectomies. Mortality was 0.8%, a severe complication occurred in 41.5%, and the failure-to-rescue rate was 2.0%. The median comprehensive complication index was 22.6 (0-100); the comprehensive complication index increased after more extensive resections. After adjustment, a pancreatoduodenectomy, as compared to a distal pancreatectomy, increased the risk for a severe complication (odds ratio 3.13 [95% confidence interval 1.32-7.41]). Of the patients with multiple endocrine neoplasia type 1 or von Hippel-Lindau, 51.9% developed a severe complication vs 38.5% with sporadic disease. After major resections, morbidity was significantly higher in patients with multiple endocrine neoplasia type 1/von Hippel-Lindau (comprehensive complication index 45.1 vs 28.9, P = .029). CONCLUSION: Surgery for pancreatic neuroendocrine tumors is associated with a high rate of complications but low failure-to-rescue in centers of excellence. Complications are procedure-specific. Major resections in patients with multiple endocrine neoplasia type 1/von Hippel-Lindau appear to increase the risk of complications.

The immune tumour microenvironment of neuroendocrine tumours and its implications for immune checkpoint inhibitors.

Immunotherapy in the form of immune checkpoint inhibitors (ICIs) has transformed the treatment landscape in numerous types of advanced cancer. However, the majority of patients do not benefit from this treatment modality. Although data are scarce, in general, patients with low-grade neuroendocrine tumours (NETs) do not benefit from treatment with ICIs in contrast to patients with neuroendocrine carcinoma, in which a small subgroup of patients may benefit. Low- and intermediate-grade NETs predominantly lack factors associated with response to ICIs treatment, like immune cell infiltration, and have an immunosuppressive tumour metabolism and microenvironment. In addition, because of its potential influence on the response to ICIs, major interest has been shown in the tryptophan-degrading enzymes indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO). These enzymes work along the kynurenine pathway that deplete tryptophan in the tumour microenvironment. IDO and TDO are especially of interest in NETs since some tumours produce serotonin but the majority do not, which potentially deplete the precursor tryptophan. In this review, we summarize the current knowledge on the immune tumour microenvironment of neuroendocrine tumours and implications for treatment with immune checkpoint inhibitors. We also discuss (targetable) factors in the NET tumour microenvironment that potentially modulate the anti-cancer immune response.

Neuroendocrine tumours and their microenvironment.

Tumours can escape the immune system by expressing programmed death-ligand-1 (PD-L1), which allows them to bind to PD-1 on T-cells and avoid recognition by the immune system. Regulatory T-cells (Tregs), indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) also play a role in immune suppression. Knowledge about the interaction of neuroendocrine tumours (NETs) with their immune microenvironment and the role of immunotherapy in patients with NET is scarce. Here, we investigated the immune microenvironment of serotonin-producing (SP) and non-serotonin-producing NETs (NSP-NETs). Tumours of 33 patients with SP-NET and 18 patients with NSP-NET were studied. Immunohistochemical analyses were performed for PD-L1, T-cells, IDO, TDO, mismatch repair proteins (MMRp) and activated fibroblasts. PD-L1 expression was seen in < 1% of tumour and T-cells. T-cells were present in 33% of NETs, varying between 1 and 10% T-cells per high power field. IDO was expressed in tumour cells in 55% of SP-NETs and 22% of NSP-NETs (p = 0.039). TDO was expressed in stromal cells in 64% of SP-NETs and 13% of NSP-NETs (p = 0.001). No tumours had loss of MMRp. TDO-expressing stromal cells also strongly expressed α-SMA and were identified as cancer-associated fibroblasts (CAFs). Factors that are associated with a response to checkpoint inhibitor treatment were absent or only present to a limited extent in the tumour microenvironment of NETs. The expression of IDO and TDO in a substantial part of NETs and the presence of CAFs suggest two mechanisms that could be responsible for the cold immune microenvironment, which should be explored to enhance anti-tumour immunity and clinical responses.