Itching, or pruritus, is a common sensation often caused by everyday factors like dry skin, allergies, or insect bites. While usually benign, persistent or unexplained itching can signal an underlying medical condition. In some cases, pruritus may be associated with certain cancers. This article explores scenarios where itching might indicate a connection to cancer.
Cancers Linked to Itching
Pruritus can be a symptom in several cancer types, particularly blood cancers like lymphomas and leukemias. Itching is common in Hodgkin lymphoma, affecting up to 20% of cases. While less common in most non-Hodgkin lymphomas, it is a frequent symptom of cutaneous T-cell lymphomas (CTCL), including mycosis fungoides and Sézary syndrome, where it can be severe.
Leukemias, such as chronic lymphocytic and chronic myeloid leukemia, can also cause itching. Aquagenic itch, which occurs after water contact without a visible rash, is often seen in polycythemia vera, a chronic blood disorder characterized by excess red blood cell production. Some individuals with polycythemia vera may later develop conditions like myelodysplastic syndrome or acute myeloid leukemia.
Solid tumors, especially those affecting the liver, bile ducts, and pancreas, can also cause itching. Cancers of the pancreas, liver, or gallbladder may obstruct bile ducts, leading to bile buildup in the bloodstream. Certain skin cancers, including melanoma, basal cell carcinoma, and squamous cell carcinoma, can cause localized itching at the site of the lesion. An itchy mole can be a warning sign for melanoma, with itching reported in 22% of primary lesions. Inflammatory breast cancer, an aggressive type, can also present with persistent itching and a rash.
The Mechanisms Behind Cancer Itching
Cancer can induce pruritus through several biological pathways. One mechanism involves paraneoplastic syndromes, where the immune system reacts to the cancer, causing symptoms distant from the tumor. This itching is not due to direct tumor invasion or compression. Paraneoplastic itching involves the release of various itch-inducing substances.
Cancer cells or the immune response can release chemicals that irritate nerve endings. For example, in lymphomas and leukemias, immune cells may release high levels of cytokines, leading to persistent itching. Histamine, a chemical associated with allergic reactions, is also implicated, particularly in polycythemia vera where its abnormal production causes itching.
Direct tumor effects can also cause itching. Some skin cancers stimulate nerve endings, causing localized itching. In cancers of the liver, pancreas, or bile ducts, a tumor can cause an obstruction. This blockage prevents normal bile flow, leading to bilirubin buildup in the bloodstream and skin, which causes itching. This itching is often accompanied by jaundice, a yellowing of the skin and eyes.
Identifying Cancer-Related Itch
Recognizing the characteristics of cancer-associated itching helps differentiate it from common causes. Itching linked to cancer is typically generalized, affecting the entire body rather than a single spot. This widespread itching often lacks a visible rash, though secondary changes like excoriations from scratching can occur.
The itch is persistent and does not typically resolve with conventional remedies like moisturizers or over-the-counter antihistamines. Cancer-related pruritus can be worse at night, disrupting sleep. Aquagenic pruritus, an itch developing after water contact without a rash, can also be a feature. While these features can suggest a potential link to cancer, itching alone is not indicative of malignancy.
When to Seek Medical Attention
While most itching is not cancer-related, new, persistent, or severe itching warrants medical evaluation. Seek attention if itching is unexplained by common causes like dry skin, allergies, or insect bites, or if it does not improve with home treatments. Any itching lasting six weeks or longer should be discussed with a healthcare professional.
Consult a doctor if itching is accompanied by other concerning symptoms. These include unexplained weight loss, fatigue, night sweats, or swollen lymph nodes. The presence of jaundice (yellowing of the skin or eyes) or changes in skin appearance like new or changing moles should also prompt a medical visit. Only a medical professional can accurately diagnose the cause of persistent itching and recommend management.