Abstract
Metabolism of neoplastic cells is shifted toward high glucose uptake and enhanced lactate production. Lactate dehydrogenase (LDH), which is comprised of two major subunits, LDH-A and LDH-B, reversibly catalyzes the conversion of pyruvate to lactate or lactate to pyruvate. LDH-A has a higher affinity for pyruvate and is a key enzyme in the glycolytic pathway. Elevated LDH is a negative prognostic biomarker not only because it is a key enzyme involved in cancer metabolism, but also because it allows neoplastic cells to suppress and evade the immune system by altering the tumor microenvironment. LDH-A alters the tumor microenvironment via increased production of lactate. This leads to enhancement of immune-suppressive cells, such as myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and dendritic cells (DCs); and inhibition of cytolytic cells, such as natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs). By promoting immune-suppression in the tumor microenvironment, LDH-A is able to promote resistance to chemo/radio/targeted therapy. Here we discuss the evidence that LDH is both a metabolic and an immune surveillance prognostic biomarker and its elevation is harbinger of negative outcome in both solid and hematologic neoplasms.