Soluble MICA appears to inhibit γδTc cytotoxicity against breast tumor targets in hypoxia and, despite their increased killing capacity under low O2, γδTc are unable to overcome resistance exhibited by MCF-7 under 2% O2 (Figure 6), a condition under which γδTc must operate within at least some parts of a tumor. This evidence concerns the gene MICA and breast neoplasm.