The appearance of a rash (visible change in skin texture or color) can be concerning, especially for individuals with a cancer diagnosis. The relationship between cancer and skin changes is complex, ranging from a direct effect of the malignancy to a side effect of aggressive treatment. A skin reaction may signal an internal tumor, be a consequence of therapy, or warn of a serious complication. Identifying the cause is the first step toward appropriate management.
Rashes Caused Directly by Cancer
Rashes occurring before treatment signify a direct connection between the malignancy and the skin. These are paraneoplastic syndromes, systemic effects caused by tumor-produced substances (hormones or peptides) that circulate and trigger a skin reaction. Necrolytic Migratory Erythema is a rare rash of bright red, blistered, and crusted areas that migrate, associated with a pancreatic tumor (glucagonoma).
Acquired Ichthyosis is a paraneoplastic condition presenting as dry, polygonal, fish-like scaling, commonly associated with Hodgkin lymphoma or other blood cancers. Treating the underlying malignancy often resolves the ichthyosis. Dermatomyositis is an inflammatory disorder characterized by a violaceous rash on the eyelids and raised, reddish bumps over the knuckles (Gottron papules). When this appears in adults, it is associated with an increased risk of internal malignancy (ovarian, lung, or pancreatic cancer).
The rash is caused by the physical infiltration of cancer cells into the skin, seen in hematological malignancies. Leukemia cutis involves leukemia cells escaping the bone marrow and forming bumpy lesions or plaques. Mycosis fungoides, a primary cutaneous T-cell lymphoma, begins as slowly progressing, itchy, patch-like lesions that can mimic common skin conditions. These direct signs may precede a cancer diagnosis by months or years, making accurate recognition valuable for early detection.
Skin Reactions Related to Cancer Treatment
Most rashes result from treatments used to destroy tumor cells. Traditional chemotherapy agents can cause generalized hypersensitivity reactions, presenting as a maculopapular rash (flat red patches mixed with small, raised bumps). Hand-Foot Syndrome (palmar-plantar erythrodysesthesia) is a challenging side effect where the hands and soles develop redness, swelling, and pain, progressing to cracking or blistering. This occurs when the drug leaks out of small blood vessels, damaging the tissue.
Targeted therapies, which block growth pathways, also cause distinct skin reactions. Drugs that inhibit the epidermal growth factor receptor (EGFR) frequently lead to an acneiform eruption, a papulopustular rash that appears acne-like but lacks the blackheads and whiteheads of true acne. This rash is common (over 50% of patients) and is sometimes viewed as a sign that the medication is working effectively. It typically develops on the face, scalp, and upper trunk within the first few weeks of treatment.
Immunotherapy (immune checkpoint inhibitors) works by activating the patient’s immune system to attack cancer cells. This systemic activation can cause inflammatory rashes by attacking healthy skin cells. These rashes can take various forms, including eczematous, lichenoid, or maculopapular eruptions, and require careful management. Radiation therapy causes radiation dermatitis, a localized skin reaction confined to the treatment field, progressing from faint redness to potential moist peeling and ulceration.
Secondary Skin Issues in Cancer Patients
A compromised immune system, due to chemotherapy, leaves patients vulnerable to opportunistic infections and rashes. Viral reactivations are common, such as Herpes Zoster (shingles), the reactivation of the chickenpox virus, causing a painful, blistering rash in a stripe pattern on one side of the body.
Fungal infections, like cutaneous candidiasis (caused by Candida yeast overgrowth), manifest as bright red, sometimes pustular, patches in warm, moist areas like skin folds. Bacterial infections, such as cellulitis, are a serious concern when the immune system is suppressed, particularly in patients with neutropenia. Cellulitis is a deep, spreading infection that causes the skin to become red, warm, and swollen, and can rapidly progress to a systemic infection.
General debilitation can lead to mechanical skin breakdown. Pressure ulcers (bedsores) form when sustained pressure cuts off blood flow to the skin, causing tissue death. They typically occur over bony prominences in immobile or severely malnourished patients. Persistent redness that does not fade when pressure is relieved indicates underlying tissue damage.
When to Seek Urgent Medical Evaluation
While many rashes are manageable side effects, some symptoms signal a medical emergency. The primary warning sign is a fever of 100.4°F (38°C) or higher accompanying any new rash. This combination indicates a rapidly progressing infection or a severe systemic drug reaction, which can become life-threatening quickly for immunocompromised patients.
Certain rare rashes demand emergency care. These include Stevens-Johnson syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), which begin with flu-like symptoms followed by a painful, rapidly spreading rash that blisters and causes the skin to peel off in sheets. A hallmark is the involvement of mucous membranes, such as painful erosions in the mouth, eyes, or genitals. Another severe reaction is Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), which presents with a rash, fever, and signs of internal organ damage, most commonly to the liver.
Patients should immediately report any rash that is rapidly spreading, accompanied by blistering or peeling, or associated with swelling of the face, tongue, or throat. Photographing the rash and noting the start date and recent medication changes is helpful. A healthcare professional must accurately distinguish a benign side effect from a life-threatening condition or one necessitating an immediate adjustment to cancer treatment.