LDH is involved in tumor initiation and metabolism.  Cancer cells rely on increased glycolysis resulting in increased lactate production in addition to aerobic respiration in the mitochondria, even under oxygen-sufficient conditions (a process known as the Warburg effect).  This state of fermentative glycolysis is catalyzed by the A form of LDH.  This mechanism allows tumorous cells to convert the majority of their glucose stores into lactate regardless of oxygen availability, shifting use of glucose metabolites from simple energy production to the promotion of accelerated cell growth and replication.
LDH A and the possibility of inhibiting its activity has been identified as a promising target in cancer treatments focused on preventing carcinogenic cells from proliferating. Chemical inhibition of LDH A has demonstrated marked changes in metabolic processes and overall survival of carcinoma cells.  Oxamate is a cytosolic inhibitor of LDH A that significantly decreases ATP production in tumorous cells as well as increasing production of reactive oxygen species (ROS).  These ROS drive cancer cell proliferation by activating kinases that drive cell cycle progression growth factors at low concentrations, but can damage DNA through oxidative stress at higher concentrations.  Secondary lipid oxidation products can also inactivate LDH and impact its ability to regenerate NADH, directly disrupting the enzymes ability to convert lactate to pyruvate.
While recent studies have shown that LDH activity is not necessarily an indicator of metastatic risk, LDH expression can act as a general marker in the prognosis of cancers.  Expression of LDH5 and VEGF in tumors and the stroma has been found to be a strong prognostic factor for diffuse or mixed-type gastric cancers.