Radioimmunotherapy represents a specialized approach in cancer treatment that combines the precision of immunotherapy with the cell-killing power of radiation. This method offers a targeted way to combat cancerous cells throughout the body. By linking two distinct therapeutic components, radioimmunotherapy aims to deliver localized treatment, potentially reducing harm to healthy tissues. It is an evolving strategy in oncology for improving patient outcomes.
Understanding Radioimmunotherapy
Radioimmunotherapy (RIT) is a targeted cancer treatment that uses monoclonal antibodies to deliver radiation directly to tumor cells. Its core components are a monoclonal antibody and a radioisotope, chemically linked to form a single therapeutic agent.
Monoclonal antibodies are laboratory-produced proteins designed to recognize and bind to specific targets, known as antigens, on cancer cells. These antibodies act as highly specific guides, leading the treatment directly to diseased cells. The radioisotope, a radioactive material, is the component that delivers the therapeutic radiation.
The two elements are joined through a process called conjugation, creating a stable compound capable of targeting cancer cells. This engineered agent, often referred to as a radiopharmaceutical or radioimmunoconjugate, is then introduced into the patient’s bloodstream. The antibody’s specificity ensures that the attached radioisotope is carried predominantly to the cancer cells.
The Mechanism of Action
Radioimmunotherapy works by leveraging the specific binding capabilities of monoclonal antibodies to deliver radiation directly to cancer cells. Once the radiolabeled antibody is administered, it circulates through the bloodstream, seeking out and attaching to specific antigens present on the surface of tumor cells. This binding ensures that the radioactive material is concentrated at the tumor site, rather than distributed broadly throughout the body.
Upon binding, the attached radioisotope emits ionizing radiation, which directly damages the DNA of the cancer cells. This DNA damage disrupts the cells’ ability to grow and divide, ultimately leading to their death. The types of radiation commonly used in RIT are beta-emitters, such as Yttrium-90 (⁹⁰Y) and Iodine-131 (¹³¹I), which release particles that travel a short distance within tissues. This short range helps to deliver a precise dose of radiation to the tumor while minimizing exposure to surrounding healthy cells.
Beyond direct cellular damage, RIT can also induce a “bystander effect,” where radiation from targeted cells can affect nearby cancer cells not directly bound by the antibody. This cross-fire effect contributes to a more comprehensive destruction of the tumor. This localized delivery of radiation aims to maximize therapeutic effect on the tumor while reducing systemic toxicity often seen with conventional radiation or chemotherapy.
Clinical Applications and Patient Considerations
Radioimmunotherapy has demonstrated effectiveness in treating specific types of cancers, particularly certain hematological malignancies. It is an approved treatment for non-Hodgkin B-cell lymphoma, especially in cases that have not responded to prior chemotherapy or the monoclonal antibody rituximab. RIT may also be considered for newly diagnosed non-Hodgkin B-cell lymphoma patients or those with other subtypes of lymphoma. Ongoing research explores its potential in other cancers, including prostate cancer, metastatic melanoma, ovarian cancer, leukemia, high-grade brain glioma, and colorectal cancer.
Patient eligibility for RIT involves several considerations. Doctors assess the patient’s overall health and the specific characteristics of their cancer, including the presence of the target antigen on the tumor cells. Diagnostic testing, often involving imaging scans like SPECT-CT or PET-CT with a low dose of radiotracer, helps to confirm the antigen’s presence and distribution. Patients with significant bone marrow involvement or those who have undergone bone marrow transplants may not be suitable candidates due to potential side effects. Pregnant or breastfeeding women are not treated with RIT.
The treatment process for RIT involves one or two sessions, administered intravenously as an outpatient procedure. Before the radioactive dose, patients receive an initial infusion of a non-radioactive monoclonal antibody, which helps protect non-malignant B cells from radiation. This initial infusion can take several hours. The therapeutic radioactive infusion is given a week later and is shorter, typically lasting an hour.
Common side effects of RIT are short-term and include fever, chills, low blood pressure, diarrhea, and rash. The most serious side effect is myelosuppression, a reduction in blood cell counts, which occurs up to a few months after treatment. This reduction increases the risk of bleeding or infection, requiring close monitoring of blood counts by the medical team. While allergic reactions are rare, their risk may increase with multiple therapies. Compared to conventional chemotherapy or external radiation, RIT results in fewer and less severe systemic side effects due to its targeted nature.