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.
Tim J Takkenkamp, Mathilde Jalving, Frederik J H Hoogwater, and Annemiek M E Walenkamp
Roeliene C Kruizinga, Wim J Sluiter, Elisabeth G E de Vries, Bernard A Zonnenberg, Cornelis J Lips, Anouk N A van der Horst-Schrivers, Annemiek M E Walenkamp, and Thera P Links
von Hippel–Lindau (VHL) mutation carriers develop benign and malignant tumors, requiring regular surveillance. The aim of this study was to calculate the optimal organ-specific age to initiate surveillance and optimal intervals to detect initial and subsequent VHL-related manifestations. In this study, we compare these results with the current VHL surveillance guidelines. We collected data from 82 VHL mutation carriers in the Dutch VHL surveillance program. The cumulative proportion of carriers diagnosed with a first VHL-related manifestation was estimated by the Kaplan–Meier method. The Poisson distribution model was used to calculate average time to detection of the first VHL-related manifestation and subsequent manifestations. We used this to calculate the optimal organ-specific age to initiate surveillance and the surveillance interval that results in a detection probability of 5%. The calculated organ-specific ages to initiate surveillance were 0 years (birth) for adrenal glands, 7 years for the retina, 14 years for the cerebellum, 15 years for the spinal cord, 16 years for pancreas, and 18 years for the kidneys. The calculated surveillance intervals were 4 years for the adrenal glands, biennially for the retina and pancreas, and annually for the cerebellum, spinal cord, and kidneys. Compared with current VHL guidelines, the calculated starting age of surveillance was 6 years later for the retina and 5 years earlier for adrenal glands. The surveillance intervals were two times longer for the retina and four times longer for the adrenal glands. To attain a 5% detection probability rate per organ, our mathematical model indicates that several modifications of current VHL surveillance guidelines should be considered.