RET and medullary thyroid gland carcinoma: MTC is reported to show low PD-L1 expression in both tumour cells and tumour-infiltrating immune cells and no microsatellite instability (Bongiovanni et al. 2017, Bi et al. 2019), irrespective of the presence or absence of either desmoplasia, lymph node metastases and/or RET mutation (Bai et al. 2019, 2020, Shi et al. 2019, Ingenwerth et al. 2020).