Mass cytometry in POEMS (polyneuropathy, organomegaly, endocrinopathy, M-protein, skin changes) syndrome: looking for a needle in a haystack In their current paper, Kourelis I et al i . profile the different immune cells within the bone marrow (BM) of patients with POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M-protein, skin changes) (Kourelis I et al. i , [8]). Different immune checkpoint regulators are expressed by HRS cells, but PD-L1 is found to be universally present on HRS cells due to a genetic amplification at chromosome 9 (De Goycoechea I et al. i , [6]). [Extracted from the article]