Cancer and blood sugar regulation are complexly linked. While high blood sugar is often discussed due to treatments or stress, cancer can also cause hypoglycemia, or low blood sugar. Hypoglycemia is defined by a drop in blood glucose levels, typically below 70 milligrams per deciliter (mg/dL). Glucose is the body’s primary fuel source, and the brain is particularly dependent on it for energy. The phenomenon of cancer causing low blood sugar is a distinct and medically significant event.
When Cancer Causes Low Blood Sugar
Cancer can directly cause low blood sugar, though this is relatively rare compared to other cancer-related complications. This effect is often categorized as a paraneoplastic syndrome, where symptoms are caused by substances secreted by the tumor or the body’s immune response, rather than the physical cancer cells themselves. While up to 20% of cancer patients may experience a paraneoplastic syndrome, tumor-induced hypoglycemia is far less common.
The types of cancer most commonly associated with this effect fall into two main groups. The first includes insulinomas, tumors originating from the pancreas’s insulin-producing cells that secrete large amounts of insulin. The second group involves non-islet cell tumors, which are often large, rapidly growing masses not originating from the pancreas. These non-islet cell tumors, such as fibrosarcomas, hemangiopericytomas, or large hepatocellular carcinomas, cause hypoglycemia through a different biological mechanism.
Biological Mechanisms of Glucose Reduction
The reduction in blood glucose levels generally occurs through two distinct pathways: ectopic production of hormone-like substances and excessive glucose consumption by the tumor itself. In cases of insulinoma, tumor cells produce and release insulin directly into the bloodstream, independent of normal regulatory signals. This excess insulin acts on muscle and fat cells, driving glucose out of the blood and leading to profound hypoglycemia.
For non-islet cell tumors, the primary mechanism often involves the secretion of a precursor form of Insulin-like Growth Factor II (IGF-II), sometimes called “big” IGF-II. This large precursor molecule is biologically active and mimics insulin by binding to insulin receptors throughout the body. The binding of “big” IGF-II stimulates cells, particularly in the muscles, to increase their uptake of glucose from the bloodstream.
This ectopic hormone production suppresses the body’s normal glucose counter-regulatory mechanisms, such as the release of glucagon and glucose production by the liver. This results in increased glucose utilization by peripheral tissues and decreased ability to generate new glucose. A second, less common mechanism involves massive tumors that consume glucose at an accelerated rate to fuel their rapid growth, leading to low blood sugar, especially during periods of fasting.
Recognizing and Managing Cancer-Related Hypoglycemia
Recognizing cancer-related hypoglycemia starts with identifying characteristic symptoms, which arise from the brain being deprived of its main energy source. Initial signs include sweating, shakiness, a rapid heart rate, and anxiety. As blood sugar drops further, symptoms progress to confusion, difficulty speaking, dizziness, and potentially seizures or loss of consciousness.
Diagnosis is confirmed using Whipple’s triad, a set of three criteria: symptoms consistent with low blood sugar, a documented low blood glucose level, and relief of symptoms when glucose is raised. Laboratory tests performed during a hypoglycemic episode help determine the specific underlying mechanism. For instance, an insulinoma shows high insulin and C-peptide, while a non-islet cell tumor shows suppressed insulin and C-peptide with an elevated IGF-II to IGF-I ratio.
Immediate management involves administering a fast-acting source of glucose, such as glucose tablets, juice, or a sugary drink. For a conscious patient, 15 to 20 grams of oral glucose is recommended, with blood sugar rechecked after 15 minutes. In severe cases where the patient is unconscious or unable to swallow, an injection of glucagon or intravenous dextrose is necessary to quickly restore blood glucose levels.
Long-term treatment focuses on addressing the underlying tumor and providing supportive care strategies. Due to the persistent nature of the hormonal effects, patients often require frequent high-carbohydrate meals and snacks, including those taken overnight, to maintain stable glucose levels. Pharmacological interventions, such as glucocorticoids (corticosteroids) or diazoxide, may be used to suppress IGF-II production or inhibit insulin secretion. The most definitive treatment for tumor-induced hypoglycemia is the complete surgical removal or cytoreduction of the tumor causing the hormonal imbalance.