Shingles, or Herpes Zoster, is a painful viral infection resulting from the reactivation of the Varicella-Zoster Virus (VZV), the same virus that causes chickenpox. After an initial chickenpox infection, VZV lies dormant in the nerve ganglia, and shingles occurs when this latent virus reawakens. A connection exists between shingles and cancer: a cancer diagnosis dramatically increases the risk of a shingles outbreak, and a shingles episode can sometimes signal the presence of an underlying malignancy.
Why Cancer Patients Are Highly Susceptible to Shingles
Shingles reactivation is typically prevented by strong cell-mediated immunity, specifically T-cells, which keep the dormant VZV in check. Cancer and its treatments compromise these defenses, creating an environment where the virus can easily reactivate.
The cancer itself can directly impair immune function, particularly in hematological malignancies such as leukemia and lymphoma. Since these cancers originate in the blood-forming tissues and lymphatic system, they disrupt T-cell production and function. Patients with these cancers face a risk of developing shingles that is more than three times higher than the general population, even before treatment begins.
Systemic cancer treatments exacerbate this vulnerability. Chemotherapy, high-dose corticosteroids, and certain novel immunotherapies deplete the population of circulating T-cells. For patients with solid tumors, such as breast or lung cancer, the increased risk of shingles is largely associated with receiving chemotherapy after their diagnosis. Overall, a cancer diagnosis of any kind is associated with approximately a 40% increased risk for developing shingles.
Investigating the Link: Does Shingles Increase Cancer Risk?
Whether a shingles episode can predict a future cancer diagnosis has been the subject of several large epidemiological studies. Current evidence suggests that shingles is not a direct cause of cancer but acts as a warning sign of an underlying health issue. The immune system’s failure to suppress the VZV indicates a pre-existing state of immunosuppression, which may be due to an occult, or undiagnosed, cancer.
Studies report a slightly increased relative risk for any cancer after a shingles diagnosis, particularly within the first year. This association is strongest for hematologic malignancies, which are known to suppress the immune system in their early stages. The elevated risk for blood cancers has been observed up to two years before the actual cancer diagnosis.
The risk of being diagnosed with cancer decreases significantly the further out a patient is from the shingles episode, often returning to the baseline of the general population within two to four years. This pattern supports the theory that the cancer was already present and weakening the body’s defenses, leading to the shingles outbreak, rather than the virus itself causing the cancer. While the absolute risk of finding a hidden cancer after shingles is low (0.7% to 1.1%), an unexpected shingles diagnosis warrants a thorough medical evaluation, especially in younger individuals.
Prevention and Treatment Considerations for Immunocompromised Patients
Preventing a shingles outbreak is a concern for individuals who are immunocompromised or are about to undergo cancer treatment. The recombinant zoster vaccine (RZV, Shingrix) is the preferred method of prevention; as a non-live vaccine, it is safe for this vulnerable population, unlike the older live attenuated vaccine. RZV is recommended for all immunocompromised adults aged 18 and older, including those with solid tumors and hematologic malignancies.
The vaccination schedule involves two doses administered intramuscularly. For immunocompromised individuals, the second dose can be given more quickly, between one and two months after the first dose, to achieve full protection sooner. Ideally, the two-dose series should be completed at least 14 days before starting any intensive immunosuppressive therapy, such as chemotherapy. If vaccination prior to treatment is not possible, it may be administered when immunosuppression is anticipated to be at its lowest point, with a medical team’s guidance.
When shingles occurs in a patient with cancer, antiviral treatment is required to prevent severe complications, such as disseminated disease or Postherpetic Neuralgia (PHN). For severe or extensive infections, intravenous (IV) acyclovir is the standard of care, administered at a dose of 10 to 15 milligrams per kilogram every eight hours for seven to ten days. This IV route ensures high drug concentrations to combat the virus effectively in a compromised system.
For less severe, localized cases, high-dose oral therapy may be considered. Oral valacyclovir, at a dose of 2 grams three times daily, can achieve plasma levels of the active drug that are comparable to those reached with IV acyclovir. Oral acyclovir (800 mg five times daily) or famciclovir (500 mg three times daily) are also options. The duration of treatment in an immunocompromised patient is often extended beyond the typical seven days, continuing until all lesions have fully crusted over, ensuring the virus is fully suppressed.