What 'Indolent' Means in a Medical Diagnosis

In medicine, the term "indolent" indicates that a disease is progressing slowly and does not pose an immediate threat. It is commonly used to describe certain cancers but can also be applied to other non-cancerous conditions.

Yet, just because a medical condition is indolent doesn't mean it should not be treated. There are times when treating an indolent condition is the better approach and others when treatment is essential.

This article looks at what "indolent" means and offers examples of common indolent conditions. It also explains why an indolent disease may or may not be treated.

What Is 'Indolent?'

The word "indolent" is used in everyday English to describe someone or something that is lazy, lethargic, or idle. When used in medicine, "indolent" describes a disease that continues without pain, symptoms, or significant progression for a long time, often years instead of months.

Certain cancers are characteristically indolent. This means that the tumor is growing slowly and you have time to make decisions about how to treat it.

The term "indolent" may be applied to any disease that is progressive but is currently not. In practice, however, it infers a disease that has the potential to become serious and may require treatment, either now or later, to prevent it from becoming so.

For instance, you wouldn't call gingivitis (a form of gum infection) indolent because you've had it a long time and don't feel anything. You would intervene whether symptoms are significant or not.

On the other hand, you would call certain prostate cancers indolent if they are slowly progressing. Even if the condition is unlikely to become serious, there is no guarantee that it won't.

To Treat or Not Treat

Having a disease that is indolent doesn't mean that it won't eventually progress and cause symptoms. In some cases, your provider will need to take a "watch-and-wait" approach (also known as active surveillance) to monitor for any changes and to act when needed.

At other times, treatment may be recommended based on the expected behaviors of the disease.

Among the reasons why treatment may be delayed:

• Low risk of progression: For instance, delaying treatment of indolent prostate cancer may be appropriate for older males who are more likely to die from other causes. Delaying also spares them the adverse effects of treatment.
• Avoiding retreatment: An indolent benign bone tumor can destabilize the hip and eventually require a hip replacement. Delaying the replacement until you are older ensures that the artificial hip will last the rest of your life, rather than wearing out and requiring retreatment.
• No survival benefit: With indolent forms of non-Hodgkin lymphoma, a type of blood cancer, early treatment has not been shown to increase life expectancy (known as the survival benefit) compared to delayed treatment.

Among the reasons why treatment may be recommended:

• High risk of disease progression: Indolent systemic mastocytosis (the overproduction of a type of immune cell in the skin called mast cells) is a slowly progressive, typically benign condition that can become suddenly aggressive in people with certain gene mutations.
• When an indolent disease is not indolent: Opportunistic infections in people with advanced HIV, particularly fungal ones, can often be indolent but need treatment regardless due to the underlying immunocompromised state. If progression were to occur, it could be devastating.
• Peace of mind: Indolent NHL can often be cured with radiation alone if the disease is limited. If you are strong and healthy, curative treatment may be reasonable as it spares you the need for chemotherapy.

While the decision to treat or not treat is ultimately a shared one, there are times when delaying may not be in your best interest.

Examples of Indolent Diseases

Many diseases can be classified as indolent. Cancer is the condition for which the term is most often used, but there are also indolent conditions that are benign (non-cancerous).

Here are several examples of indolent diseases, both common and uncommon:

• Non-Hodgkin lymphoma (NHL): Indolent NHL accounts for 40% of NHL cases and includes cutaneous T-cell lymphoma, follicular lymphoma (FL), lymphoplasmacytic lymphoma, Waldenström macroglobulinemia, marginal zone lymphoma, small cell lymphocytic lymphoma (SLL), and chronic lymphocytic leukemia (CLL). Active surveillance is often recommended.
• Prostate cancer: The majority of prostate cancers follow an indolent course. Because there are risks to overtreating indolent prostate cancer, such as loss of sexual function and incontinence, active surveillance is often recommended.
• Indolent breast cancer: This is a rare form of breast cancer, which some studies suggest has a 15-year survival rate of 100%. People with indolent breast cancer may be treated with hormonal therapy rather than chemotherapy in the early stages.
• Indolent tuberculosis (TB): Latent tuberculosis occurs when the immune system is able to control the bacteria that causes TB (Mycobacterium tuberculosis), often for decades. Even so, the infection is typically treated as 10% to 15% of cases will progress to symptomatic TB.
• Carcinoid tumors: These are slow-growing cancers that usually start in the digestive tract or lungs and can spread (metastasize) to other organs. While carcinoid tumors are often indolent, surgery would still be recommended to remove the tumor and reduce the risk of metastasis.
• Indolent systemic mastocytosis: Indolent systemic mastocytosis is the mildest form, mainly affecting the skin. While the risk of progression is low, people with certain cell lines and gene mutations can develop severe disease affecting multiple organs.
• Pituitary adenoma: This is a benign, slow-growing tumor affecting the pituitary gland. Pituitary adenomas are often indolent, but when the tumor gets large enough, it can cause the disruption of multiple hormones, leading to symptomatic hypopituitarism.
• Indolent carditis: This is a heart condition that can develop as a result of rheumatic fever, causing inflammation of the heart's inner lining (endocarditis) and often with a total lack of symptoms. Though slowly progressive, it can cause serious heart valve problems over time.
• Leprosy: This is a rare chronic infection caused by a non-tuberculosis form of Mycobacterium. Also known as Hansen's disease, leprosy is typically indolent in the early years before disfiguring skin sores and other symptoms develop. Leprosy is curable with a course of antibiotics.
  

Summary

An indolent disease is one that persists for a long time without significant progression and without pain or other notable symptoms.

In some cases, an indolent disease requires treatment, either because the risk of progression is high or the benefits of treatment outweigh the risks. At other times, healthcare providers will take a watch-and-wait approach, either because the risk of progression is low or the risks of treatment outweigh the benefits.