Currently, after surviving a primary malignancy, between 17 and 19% of patients develop a second malignancy. Secondary malignancies are cancers caused by treatment with radiation or chemotherapy. They are not related to the first cancer that was treated and may occur months or even years after initial treatment. Some treatments increase the risk of developing a second cancer, such as etoposide chemotherapy drugs, radiation therapy for some lymphomas and childhood leukemia, and treatment with radiation therapy and chemotherapy together.
Preventing secondary malignancies involves avoiding these treatments that clearly increase the risk of second cancers and ensuring that you don't get too much treatment for your particular disease or risk factors. Stereotactic RT delivers a high dose of radiation to the tumor while reducing the dose to normal tissues and may lower the risk of a second cancer (20). The risk of RT-induced breast cancer in patients treated for Hodgkin lymphoma increases if the patient's age at the time of radiation exposure is closer to menarche. For example, a patient with breast cancer or Hodgkin's disease may develop acute leukemia years after completing treatment for their first cancer.
The risk of esophageal cancer increases in patients who have undergone RT for Hodgkin and non-Hodgkin lymphomas, breast cancer, lung cancer, and previous esophageal cancer (4) Children exposed to radiation or chemotherapy have more years to live, giving them more opportunities to develop another cancer. In addition to treating cancer, chemotherapy drugs and radiation therapy are also carcinogenic, meaning they can cause cancer. For a second primary cancer to be correctly classified, metastatic lesion or local recurrence of the original primary cancer must be ruled out. Because some patients selected to receive radiation after mastectomy have a poorer prognosis than other patients, there is quite a possibility that there is a bias in the risk estimates of contralateral breast cancer that can be attributed to radiation therapy.
While the risk of a second cancer is a serious consideration when considering treatment options, it is important to know how advances in cancer treatment can allow doctors to limit this threat. While radio-induced cancers have been well known since the early years of the 20th century, they were not a major concern for radiation oncologists for many decades. It's not possible to predict who might have a second cancer, but sometimes cancer treatment can put a person at greater risk of developing a second cancer. This had allowed a significant decrease in deterministic effects and should also lower the risk of radio-induced second cancers in areas receiving high doses of radiation.
Some drugs used to treat cancer are called targeted therapy drugs because they are designed to detect and attack certain genes or proteins found in specific types of cancer.