A complex connection exists between cancer and metabolic health, particularly involving the development of diabetes. While diabetes is a known risk factor for certain cancers, the reverse is also true: cancer and its treatments can directly cause a new onset of diabetes, often termed secondary diabetes. This metabolic complication significantly impacts a patient’s well-being and their response to cancer therapy.
Cancer Pathology Directly Affecting Glucose Control
The presence of a cancerous tumor can directly impair the body’s ability to regulate blood sugar, even before treatment begins. This is most clearly seen in pancreatic cancer, where the tumor originates near the organ responsible for producing insulin. The growing tumor can physically destroy the insulin-producing beta cells within the islets of Langerhans.
The loss of insulin-producing capacity leads to pancreatogenic diabetes, also known as Type 3c diabetes. Approximately half of people with pancreatic ductal adenocarcinoma will also have diabetes. The new onset of diabetes can sometimes be one of the first signs of the underlying malignancy.
The cancer itself can release inflammatory molecules called cytokines into the bloodstream. These molecules create chronic systemic inflammation, which interferes with how tissues like muscle and fat respond to insulin. This condition, known as insulin resistance, forces the pancreas to produce more insulin to maintain normal blood sugar levels. Over time, this sustained stress on the remaining beta cells can lead to their exhaustion and eventual failure, resulting in hyperglycemia.
Other forms of cancer can also induce metabolic changes that contribute to diabetes. Tumors may cause profound wasting and weight loss, called cachexia, which alters muscle and fat metabolism. This metabolic shift is often accompanied by increased insulin resistance, making the body’s tissues less sensitive to insulin’s action. Certain rare tumors can also directly secrete hormones that counteract insulin, further driving blood sugar levels upward.
Metabolic Side Effects of Cancer Treatments
Beyond the disease itself, cancer treatments are a frequent cause of secondary diabetes. High-dose corticosteroids, such as dexamethasone or prednisone, are a major culprit, commonly used to manage inflammation, nausea, or allergic reactions. These medications increase insulin resistance, causing the liver to produce more glucose and peripheral tissues to take up less. This effect often results in hyperglycemia that is most pronounced after meals.
Specific classes of chemotherapy and targeted therapies also carry risks of metabolic disruption. Some cytotoxic drugs, including 5-fluorouracil and platinum-based agents, have been reported to cause hyperglycemia. Newer treatments, like immune checkpoint inhibitors, can rarely cause a sudden onset of insulin-deficient diabetes similar to Type 1 diabetes. This occurs because the treatment mistakenly directs the immune system to attack and destroy the insulin-producing beta cells in the pancreas.
Surgical removal of a tumor, particularly a partial or total pancreatectomy, physically removes the body’s source of insulin, making diabetes an inevitable outcome. Radiation therapy directed at or near metabolic organs like the pancreas or liver can cause tissue damage and scarring. This damage can impair the function of the beta cells or reduce the liver’s ability to properly process glucose, contributing to new or worsened diabetes.
Diagnosing and Managing Secondary Diabetes
The diagnosis of secondary diabetes in a person with cancer can be challenging, as symptoms of high blood sugar, such as fatigue or increased thirst, often overlap with cancer or treatment side effects. Physicians often screen for new-onset diabetes by checking baseline blood glucose and a long-term marker like HbA1c before starting cancer treatment, especially if high-risk therapies like steroids are planned. Monitoring blood sugar levels is a continuous process, as treatment-induced hyperglycemia can be transient or permanent.
Management goals often differ from traditional diabetes care, prioritizing quality of life and avoiding complications that could delay cancer treatment. Aggressive glucose control is sometimes avoided to prevent dangerously low blood sugar, or hypoglycemia, which is risky for patients with poor appetite or nausea. A multidisciplinary team, including oncologists, endocrinologists, and dietitians, is often involved to tailor the diabetes regimen.
Insulin is a frequent choice for managing secondary diabetes, especially when patients are on steroids, because it offers the flexibility needed to adjust for fluctuating blood sugar levels. For some patients, the diabetes resolves once cancer treatment is completed and the causative medication is stopped. However, for others, particularly those who suffered pancreatic damage or already had risk factors for Type 2 diabetes, the condition may require long-term management.