One of the most common fears when a person hears the phrase “cancer treatment” is the idea of losing their hair, feeling extremely weak, or feeling that the whole body is affected by the therapy. That fear is understandable. For many years, the public image of cancer treatment has been closely associated with chemotherapy: nausea, fatigue, hair loss, low defenses, and the feeling that the treatment attacks not only the cancer, but also the patient’s healthy cells.

However, not all cancer treatments work in the same way. Some therapies are systemic, meaning they circulate throughout the body. Others are local or regional, which means they are directed toward a specific area. Intratumoral immunotherapy belongs to this second concept: it is designed to administer immune-stimulating agents directly inside the tumor, with the goal of activating the immune response exactly where the cancer is located.

This difference in mechanism of action is key to understanding why intratumoral immunotherapy does not usually cause hair loss or weaken the body in the same way as some chemotherapies.

Classic chemotherapy acts mainly against cells that multiply rapidly. This is useful because many cancer cells divide at an accelerated rate. The problem is that the body also has healthy cells that divide constantly, such as those in the hair follicles, bone marrow, and the lining of the digestive system. For this reason, some chemotherapy drugs can affect these areas and cause side effects such as hair loss, anemia, low defenses, nausea, diarrhea, or mouth sores.

Hair loss occurs because hair follicles are very active structures. To produce hair, their cells must divide continuously. When a drug interferes with cell division, the follicle can temporarily stop its activity and the hair falls out. This does not necessarily mean that the damage is permanent, but it can be emotionally difficult for many patients.

Intratumoral immunotherapy works from a different logic. Instead of directly attacking all rapidly dividing cells, it seeks to modify the tumor environment and help the immune system recognize it better. By being applied directly inside the tumor, its action is concentrated in the place where the disease is located. This reduces unnecessary exposure of other tissues, such as hair follicles or bone marrow.

For this reason, hair loss is not an expected effect of intratumoral immunotherapy in the same way that it can occur with chemotherapy. The treatment is not designed to block cell division throughout the body or to directly affect hair follicles. Its intention is more specific: to activate or reinforce the immune response at the tumor site.

Something similar happens with the idea of “weakening the body.” Many people associate cancer treatment with feeling without energy, with low defenses, or with a higher risk of infections. This can happen with therapies that affect the bone marrow, which is the tissue responsible for producing white blood cells, red blood cells, and platelets. When the bone marrow is suppressed, the patient may have a higher risk of infections, anemia, fatigue, or bleeding.

Intratumoral immunotherapy does not usually act in that way. It is not designed as a therapy that suppresses the bone marrow or as a treatment that globally reduces the body’s defenses. In fact, its purpose is almost the opposite.

Figure 1. Chemotherapy may affect healthy rapidly dividing tissues, contributing to side effects such as hair loss, anemia, and fatigue. Intratumoral immunotherapy is delivered directly into the tumor to activate a local immune response while reducing broader systemic exposure.

This does not mean that intratumoral immunotherapy is completely free of side effects. No major medical treatment is. By activating the immune system locally, discomfort may appear in the treated area, as well as inflammation, pain, redness, low-grade fever, temporary tiredness, or symptoms similar to those of an inflammatory response. These effects depend on the type of drug used, the dose, the size of the tumor, the location of the tumor, and the patient’s overall condition.

It is also important to differentiate intratumoral immunotherapy from systemic immunotherapy. Some immunological treatments, such as immune checkpoint inhibitors administered intravenously, can activate the immune system throughout the body. This can be beneficial against cancer, but it can also cause immune-related effects in healthy organs, such as the skin, intestine, liver, lung, or endocrine glands.

Intratumoral administration attempts to reduce that problem. The logic is that, if the treatment is concentrated where the tumor is, a more localized response can be pursued and systemic exposure can potentially be reduced. Even so, the patient must be carefully evaluated and monitored, because the immune response can vary between individuals. Intratumoral immunotherapy must be performed with medical planning, usually with image guidance, precise anatomical knowledge, and appropriate patient selection. Safety depends on many factors.

For patients and their families, this distinction can bring reassurance. Not all cancer treatments necessarily involve hair loss. Not all of them act like chemotherapy. Not all of them produce the same side effects. Each therapy has a different mechanism, and understanding that mechanism helps reduce fears and mistaken expectations. 

Main reference: Dana-Farber Cancer Institute. (2016, February 10). What are the side effects of immunotherapy? Dana-Farber Cancer Institute. https://blog.dana-farber.org/insight/2016/02/what-are-the-side-effects-of-immunotherapy/

Other references:

Haslam, I. S., & Smart, E. (2019). Chemotherapy-Induced Hair Loss: The Use of Biomarkers for Predicting Alopecic Severity and Treatment Efficacy. Biomarker insights, 14, 1177271919842180. https://doi.org/10.1177/1177271919842180

Ramos-Casals, M., Brahmer, J. R., Callahan, M. K., Flores-Chávez, A., Keegan, N., Khamashta, M. A., Lambotte, O., Mariette, X., Prat, A., & Suárez-Almazor, M. E. (2020). Immune-related adverse events of checkpoint inhibitors. Nature reviews. Disease primers, 6(1), 38. https://doi.org/10.1038/s41572-020-0160-6