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It's not possible to predict who might get a second cancer, but sometimes having cancer treatment can put a person at higher risk for second cancers. As more new treatments emerge and standard treatments continue to be used, studies continue to look at how genetics and different cancer treatments interact, as well as links between the treatments, lifestyle habits, and known cancer-causing agents.

Risk of developing second cancers after radiation therapy

Radiation therapy was recognized as a possible cause of cancer many years ago. In fact, much of what we know about the health effects of radiation has come from studying survivors of atomic bomb blasts in Japan. We also have learned from workers in certain jobs that included radiation exposure, and patients treated with radiation therapy for cancer and other diseases.

Leukemia and myelodysplastic syndrome

Past radiation exposure is one risk factor for most kinds of leukemia, including acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), and acute lymphoblastic leukemia (ALL). Myelodysplastic syndrome (MDS), a bone marrow cancer that can turn into acute leukemia, has also been linked to past radiation exposure. The risk of these diseases after radiation treatment for cancer depends on a number of factors, such as:

• How much of the bone marrow was exposed to radiation
• The amount of radiation that reached the bone marrow
• The radiation dose rate (how much was given in each dose, how long it took to give the dose, and how often it was given)

Most often, these cancers develop within several years of a person's radiation treatment. Then the chance of developing a new cancer slowly declines over the following years.

Solid tumors

There is also a risk for other cancers, which are mostly solid tumors, after having radiation therapy. Most of these cancers develop 10 years or more after radiation therapy. The effect of radiation on the risk of developing a solid tumor cancer depends on factors such as:

• The age of the patient when they were treated with radiation. For example, the risk of developing breast cancer after radiation is higher in those who were treated when they were young compared with those given radiation as adults. The chance of developing breast cancer after radiation seems to be highest in those exposed as children. Risk decreases as the age at the time of radiation increases; women who had radiation after the age of 40 have a lower risk of breast cancer. Your age when you get radiation treatment has a similar effect on the development of other solid tumors, including lung cancer, thyroid cancer, bone sarcoma, and gastrointestinal or related cancers (stomach, liver, colorectal, and pancreatic).
• The dose of radiation. In general, the risk of developing a solid tumor after radiation treatment goes up as the dose of radiation increases. Some cancers require larger doses of radiation than others, and certain treatment techniques use more radiation.
• The area treated. The area treated is also important, since these cancers tend to develop in or near the area that was treated with radiation. Certain organs, such as the breast and thyroid, seem to have a higher risk for developing cancers after exposed to radiation than other organs.

• Alkylating agents (mechlorethamine, chlorambucil, cyclophosphamide, melphalan, lomustine, carmustine, busulfan)
• Platinum-based drugs (cisplatin, carboplatin)
• Anthracycline topoisomerase II inhibitors (etoposide or VP-16, teniposide, mitoxantrone)