In summary, RNA FISH analysis of 35 XIST-positive primary breast tumors of the luminal, HER2+, and basal-like subtypes, revealed that all three X-linked genes tested, HDAC8, TBL1X, and even ATRX, show Xi reactivation in a significant proportion of tumor cells in stark contrast to the situation in healthy breast tissue from the same patient. The gene discussed is HDAC8; the disease is neoplasm.