Under normoxic conditions, the cell proliferation rate decreased after suppression of LDH-A, and under hypoxia conditions (0.5% oxygen), tumor cell growth with LDH-A deficiency was also severely impaired; tumor cells with reduced LDH-A activity could not maintain high levels of ATP, which probably contributed to the slowing of cell proliferation under normoxic or hypoxic conditions. The gene discussed is LDHA; the disease is neoplasm.