This is the product of the work of a group of physicians specialized in Internal Medicine. The result of the clinical observation in a patient with lymphoma served as support for the generation of two review articles in international journals specialized in medicine with editorial arbitration whose primary objective was to disseminate to the medical community the association between neoplasms or tumors and the generation of lactic acid. The content and bibliographic support on the physiopathology of the alteration of the acid-base balance and tumors are presented. The first chapters include the most frequent hematological tumors, among which lymphomas and leukemias stand out. There follows a chapter on multiple myeloma and another on tumors of different organs and tissues. Finally, there is a chapter on tumors and hepatic insufficiency associated with lactic acidosis.