TKTL1 and malignant colon neoplasm: Transketolase-like-1 (TKTL1) is a rate-limiting enzyme in the non-oxidized part of the PPP [9].The TKTL1 gene is located on chromosome Xq28, which is often activated in malignant tumors [10]. Studies have shown that TKTL1 is responsible for about 60–70% of TKT activity in human liver and colon cancer cells [11–13].