Therefore, we examined the plasma membrane expression of the stress-induced tumor antigens MICA, MICB, ULBP1, ULBP2 and ULBP3 (collectively termed NKG2DLs) on the tumor spheroids for comparison with the expression levels found in the corresponding parental monolayer cultures (Figure 2A, Additional file 2: Figure S1, representative histograms Additional file 2: Figure S1B). Here, ULBP2 is linked to neoplasm.