Cancer significantly increases the risk of developing severe fungal infections. This vulnerability arises because both the cancer itself and its treatments compromise the body’s natural defense systems. These infections are typically opportunistic, meaning common fungi that rarely cause illness in healthy individuals seize the chance to invade when immune function is suppressed. Understanding the mechanisms behind this immunosuppression is crucial for managing the health and safety of people undergoing cancer care.
How Cancer Disease States Weaken the Immune System
Malignant tumors directly suppress the body’s ability to fight off foreign invaders. Cancers that originate in the blood or bone marrow, such as leukemia and lymphoma, are particularly disruptive to the immune system. These malignancies can crowd out the production of healthy white blood cells, directly leading to a deficiency in infection-fighting cells like neutrophils, a condition known as neutropenia.
Cancer-associated cachexia, a wasting syndrome, further impairs immune function through systemic inflammation. The tumor releases pro-inflammatory signaling molecules, such as certain interleukins and tumor necrosis factor, which create an imbalance of cytokines in the body. This chronic inflammatory state can reduce the responsiveness of immune cells to signals that would normally activate them to destroy pathogens.
The tumor microenvironment is also designed to actively shield cancer cells from immune attack. Tumors recruit specialized immune cells, such as regulatory T cells, which suppress the anti-tumor response and dampen overall immune activity. This localized suppression allows the cancer to grow unchecked and contributes to systemic immune dysfunction, increasing susceptibility to opportunistic fungal invasion.
Immune Suppression Caused by Cancer Therapies
While the disease itself weakens immunity, cancer treatments are often the most profound and immediate cause of severe immunosuppression. Cytotoxic chemotherapy drugs kill rapidly dividing cells, including healthy precursor cells in the bone marrow that generate new blood cells. The resulting temporary but severe drop in neutrophil counts (neutropenia) is recognized as the single biggest risk factor for invasive fungal disease.
Radiation therapy can also compromise the immune system, particularly when the treatment field includes large areas of bone marrow or lymph nodes. This localized damage can reduce the number of circulating immune cells, though the effect is generally less systemic than that caused by intensive chemotherapy.
The most extreme form of therapeutic immunosuppression occurs with allogeneic hematopoietic stem cell transplantation (HSCT). This procedure requires the complete ablation of the patient’s existing immune system. Patients then undergo months of recovery and take ongoing medications to prevent graft rejection, placing them in the highest risk category for fungal infections.
Newer treatment approaches, including targeted therapies and immunotherapies, can also disrupt the delicate balance of the immune system. For instance, certain targeted drugs or long-term high-dose steroid use can impair T-cell function, which is necessary for coordinating a defense against many fungi. The use of central venous catheters, which are necessary for delivering many of these treatments, also creates a direct portal for microbes to enter the bloodstream, further compounding the infection risk.
Identifying Common Fungal Infections in Cancer Patients
Candidiasis, caused by Candida species, is the most common fungal infection in people with cancer. It often presents as a superficial infection, such as oral thrush or esophagitis, causing pain and difficulty swallowing, especially in patients with mucosal damage from chemotherapy or radiation.
However, Candida can also become invasive, leading to candidemia, where the fungus enters the bloodstream and disseminates to vital organs. A more dangerous threat, particularly for those with prolonged neutropenia, is invasive aspergillosis, caused by the mold Aspergillus. This infection is typically acquired by inhaling spores from the environment and most frequently manifests as a severe form of pneumonia, often causing tissue damage and blood clots in the lungs.
Other fungal pathogens also pose a significant threat to immunocompromised patients. Pneumocystis jirovecii, a fungus-like organism, commonly causes pneumonia, especially in patients with lymphoma or those receiving high doses of corticosteroids. While less frequent than Candida or Aspergillus, Cryptococcus neoformans is a concern because it often affects the central nervous system, causing meningitis.
Clinical Management and Prevention
Diagnosing fungal infections in cancer patients is challenging because initial symptoms are often non-specific. Fever, cough, chest pain, and fatigue are common signs of invasive fungal disease, but these symptoms can easily be mistaken for side effects of chemotherapy or the underlying cancer. Specialized diagnostic tests, such as blood assays for fungal cell components or high-resolution CT scans of the lungs, are often required to confirm the presence of an invasive infection.
Once diagnosed, treatment involves targeted antifungal medications, with the specific drug chosen based on the type of fungus identified. However, the focus in high-risk patients often shifts to prevention, known as antifungal prophylaxis. Prophylactic antifungal medication is routinely given to patients undergoing the most intensive treatments, such as allogeneic stem cell transplantation or induction chemotherapy for acute leukemia, to significantly reduce the incidence of invasive fungal infections and related mortality.
Patients and their caregivers are advised to take environmental precautions to limit exposure to fungal spores. Simple actions, such as avoiding areas of dust and mold like construction sites or stagnant water, can reduce the risk of inhaling organisms like Aspergillus. Maintaining meticulous hygiene and promptly reporting any non-resolving fever or new symptoms to the oncology team are important steps in preventing a localized infection from becoming systemic.