Second cancers are not a metastasis, or spread, of the original cancer. Second cancers are unique, additional cancers that start in a different organ or part of the body. They are also known as secondary cancers or second primary cancers. (Primary cancer is the name given to the first cancer; second cancers are new cancers not related to the first cancer). The National Cancer Institute estimates that nearly one in five cancers diagnosed today occurs in a person who has had a previous diagnosis of cancer. Second cancers are also different from a recurrence of cancer, which refers to cancer that has come back after treatment.1,2
Risk factors
Having lung cancer may indicate a higher risk of cancers in nearby organs because nearby organs are exposed to the same carcinogens, or cancer-causing agents, that led to the first cancer. For example, smoking is the number one cause of lung cancer. Smoking also increases the risk of developing cancer of the larynx (voice box), mouth, throat, and esophagus (connects the throat to the stomach).1
Some people are at an increased risk of second cancers due to an inherited genetic mutation (gene mutation passed down from parents). Damage to the genes cause normal cells to change and become cancer cells. Mutations can be inherited or caused by other factors, such as environmental exposure to pollutants like tobacco smoke. Only about 5-10% of all cancers result from genetic mutations. These inherited genetic mutations are known as family cancer syndrome. Family cancer syndromes increase the risk of developing several different kinds of cancer.1,2
Treatment-related second cancers
Some types of treatment for cancer increase the risk of developing a second cancer later on. It is well documented that radiation therapy is a potential cause of cancer. Most kinds of leukemia can be caused by past radiation exposure. Myelodysplastic syndrome (MDS), a cancer of the bone marrow, is also linked to past radiation exposure. These second cancers are most likely to occur 5-9 years after exposure. Radiation therapy also increases the risk of solid tumor cancers (solid tumor cancers are malignant masses in the body tissue, such as lung cancer; liquid tumor cancers can affect the blood and bone marrow, such as leukemia). Solid tumors generally take longer to develop and are often seen 10 years or more after radiation therapy. The area of the body that was treated with radiation is important, as solid tumors are more likely to occur in nearby organs. Additional factors can increase this risk: smoking increases the risk of lung cancer after radiation at a greater rate than without radiation.1
Some chemotherapy drugs have been linked to second cancers, particularly myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). Stem cell transplants (also may be known as bone marrow transplants), in which high doses of chemotherapy are given with or without radiation before an infusion of blood stem cells, are linked to an increased risk of second cancers due to the chemotherapy agents and radiation used.1
Ongoing research
There is ongoing research to uncover more about second cancers. Scientists are studying how lifestyle and environmental factors affect second cancers, as well as looking into inherited genetic susceptibility (gene changes causing a higher likelihood of cancer) for second cancers. Other studies are looking at how certain genetic mutations in combination with treatment for a primary tumor may put a person at a higher risk of developing a second cancer.2