Cholesterol is an amphiphilic molecule required for membrane integrity, formation of lipid microdomains, and as a biosynthetic precursor for steroid hormones, bile acids, and vitamin D. Clinical evidence indicates that hypocholesterolemia is common in many hematological malignancies and associates with disease onset, progression, response to therapy, and prognosis. Tumor-related reductions in plasma cholesterol likely result from disturbed lipoprotein metabolism, liver dysfunction driven by systemic inflammation, and altered cholesterol uptake and efflux by malignant cells. This metabolic phenotype supports tumor proliferation, fosters therapy resistance, and reprograms the immune microenvironment by impairing T-cell function and favoring M2-like macrophage polarization. Emerging strategies that target cholesterol metabolism show preclinical promise as diagnostic and therapeutic tools. The full article further details biosynthesis, uptake, excretion, conversion, regulatory networks, subtype-specific cholesterol alterations, mechanisms of hypocholesterolemia, and clinical implications; the supplied excerpt ends before full presentation of subtype data and agent tables.
Tumor cells rewire metabolism to satisfy increased biosynthetic and energetic needs. Cholesterol plays multiple roles in this reprogramming: it maintains membrane fluidity and integrity, supports membrane microdomain (lipid raft) formation, and serves as a precursor for key bioactive molecules. Intracellular cholesterol balance is maintained by synthesis, uptake, efflux, conversion, esterification, and trafficking. Observational studies show serum cholesterol begins declining years before some cancers are clinically detected, implicating cholesterol as a potential early biomarker. Understanding cholesterol biology in hematologic malignancies may reveal mechanistic insights, biomarkers for early detection and risk stratification, and targets for novel therapies.
An integrated view of cholesterol homeostasis encompasses four major processes: synthesis, absorption, transformation, and clearance. These processes collectively sustain membrane structure, enable signal transduction, and maintain systemic homeostasis.
Cholesterol (C27H46O) is a sterol composed of fused rings with a 3β-hydroxyl group and an eight-carbon side chain. In plasma, cholesterol exists as free cholesterol (FC, ~30%) and cholesteryl esters (CE, ~70%), the latter formed by LCAT and residing in the core of lipoproteins. Lipoprotein carriers include chylomicrons (CM), VLDL, IDL, LDL, and HDL, which determine cholesterol transport and tissue delivery.
De novo cholesterol synthesis occurs in most cells but predominantly in the liver. The mevalonate (MVA) pathway and subsequent squalene synthesis involve about 30 enzymatic steps. Rate-limiting enzymes include HMG-CoA reductase (HMGCR) and squalene epoxidase (SQLE), which catalyze key committed reactions. Upregulation of these enzymes supports increased cholesterol demands in proliferating tumor cells.
Dietary and biliary cholesterol are absorbed by enterocytes via NPC1L1, esterified by ACAT2, and packaged into chylomicrons for delivery to the circulation and the liver. Unesterified cholesterol can be effluxed back to the lumen by ABCG5/G8, which limits net absorption. Peripheral tissues obtain exogenous cholesterol through receptor-mediated uptake, primarily via LDLR and SR-BI.
Cholesterol is converted into bile acids in the liver (classical pathway initiated by CYP7A1 accounts for most conversion; alternative CYP27A1/CYP7B1 pathway supplements bile acid synthesis under certain conditions). It is also a precursor for steroid hormones (CYP11A1-mediated conversion to pregnenolone) and vitamin D precursors in skin. Systemic clearance relies mainly on HDL-mediated reverse cholesterol transport—nascent HDL acquires cholesterol from peripheral cells via ABCA1/ABCG1, LCAT esterifies FC to CE, and cholesteryl esters are delivered to the liver via SR-BI or CETP-mediated transfer to ApoB-containing lipoproteins for LDLR-mediated hepatic uptake and clearance.
Cholesterol contributes 20–30% of membrane lipids and buffers membrane phase transitions. It organizes lipid rafts that act as signaling platforms for receptor clustering and signal transduction. Cholesterol directly modulates ion channels and binds proteins such as Patched-1 and Smoothened to regulate Hedgehog signaling. In hematologic malignancies, cholesterol-dependent signaling supports oncogenic pathways including PI3K/Akt, Hedgehog/GLI, T-cell receptor (TCR) signaling, and LRP8/mTORC1. Deficiency or reprogramming of cholesterol metabolism can activate adaptive survival programs in tumor cells, facilitate leukemia stem cell self-renewal, promote myeloma and lymphoma progression, induce T-cell exhaustion, and confer chemotherapy resistance.
Two transcriptional families, sterol regulatory element-binding proteins (SREBPs) and liver X receptors (LXRs), coordinate intracellular cholesterol balance. SREBPs (particularly SREBP2) induce expression of genes for cholesterol synthesis and uptake, including HMGCR and LDLR. LXRs activate genes that promote efflux (ABCA1, ABCG1) and transport back to the liver. Under low cholesterol, SREBP activation upregulates synthesis and uptake; when cholesterol is high, LXRs stimulate efflux and excretion, forming a feedback loop.
In hematologic malignancies, this regulatory circuit is skewed: SREBP2 is frequently activated (noted in AML, DLBCL, and MM) to increase LDLR/HMGCR/SQLE expression and maximize uptake and synthesis, while LXR-driven efflux pathways are suppressed, reducing ABCA1/ABCG1 activity. This polarized adaptation—sustained SREBP2 activity combined with LXR repression—ensures a steady cholesterol supply for rapid membrane biosynthesis and oncogenic signaling, and contributes mechanistically to the hypocholesterolemia observed clinically.
Cell-type-specific roles are evident: SREBP supports T-cell lipid-raft integrity and TCR signaling, with impaired SREBP in chronic lymphocytic leukemia linked to reduced LDLR and T-cell exhaustion; SREBP2 promotes M1 polarization in macrophages, while low-cholesterol conditions favor M2-like tumor-associated macrophages; LXRs exert anti-inflammatory and efflux-promoting effects that vary by context. Together these interactions create a metabolic-immune network relevant to tumor progression and therapeutic targeting.
The review highlights that hypocholesterolemia is commonly observed across various hematologic cancers and may present years before clinical diagnosis in some malignancies. The supplied excerpt references clinical correlations and tabulated data (Table 1: cholesterol levels and clinical correlation; Table 2: agents targeting cholesterol metabolism) but does not include the detailed numeric or subtype-specific results in the provided text. Mechanisms proposed for tumor-associated hypocholesterolemia include dysregulated lipoprotein metabolism, inflammatory liver dysfunction, and enhanced tumor cell uptake with reduced efflux. These alterations not only reflect disease biology but also actively contribute to tumor cell proliferation, therapy resistance, and immune dysregulation. The full article likely provides subtype-specific cholesterol changes, clinical correlations, and a catalogue of therapeutic agents targeting cholesterol metabolism; those specific details were not present in the excerpt supplied.
Note: The provided source text ends partway through the section on cholesterol levels across malignancy subtypes. Tables, figures, and some clinical detail referenced in the original review are cited but their contents were not included in the excerpt available for this rewrite.