Every organ can be affected by acute side effects of anti-leukemic chemotherapy, the most common being opportunistic infections, mucositis, central or peripheral neuropathy (or both), bone toxicities (including osteonecrosis, ON), thromboembolism (TE), sinusoidal obstruction syndrome (SOS), endocrinopathies (especially corticosteroid-induced adrenal insufficiency and hyperglycemia), high-dose methotrexate (HD-MTX)-induced nephrotoxicity, asparaginase-associated hypersensitivity, pancreatitis, and hyperlipidemia. The gene discussed is ASPG; the disease is mucositis.