Previous cancer treatment as a risk factor for a second cancer

Yes — certain treatments used to cure the first cancer can, in a small number of cases, increase the risk of a different cancer appearing years or even decades later. This is called a therapy-related or treatment-induced second cancer. It is important to understand that this risk is real but relatively small, and that treatment decisions are made because the benefit of curing the first cancer far outweighs the risk. Knowing about this risk is the first step toward surveillance — which means finding and treating any second cancer at its earliest, most manageable stage.

Two categories of treatment are most strongly associated with a higher second cancer risk. First, certain chemotherapy drugs — particularly alkylating agents and a class called topoisomerase II inhibitors — can damage the DNA of healthy bone marrow cells, raising the risk of therapy-related leukaemia or myelodysplastic syndrome, typically within 5 to 10 years of treatment. Second, radiation therapy — especially high-dose radiation delivered to the chest, head, or neck during childhood — can increase the risk of solid tumours (such as breast cancer or thyroid cancer) in the tissues that were in the path of the radiation beam. The risk depends on the dose, the age of the child at the time of treatment, and the specific area treated.

The timing varies by treatment type. Therapy-related leukaemias linked to certain chemotherapy drugs typically appear within 5 to 10 years of treatment. Solid tumours caused by radiation — such as breast cancer in women who received chest radiation for Hodgkin lymphoma as children — often appear later, sometimes 10 to 30 years after treatment. This is why childhood cancer survivor follow-up continues for many years after a child is considered cured. Regular check-ups and age-specific screening allow the care team to identify any new concern at the earliest stage.

No. The risk varies significantly depending on the type of first cancer, the specific drugs and doses used, the radiation fields involved, and the child’s individual characteristics. Many childhood cancer survivors complete treatment and live their entire lives without developing a second cancer. The goal of late-effects surveillance is not to alarm survivors — it is to monitor them appropriately so that if a second cancer does appear, it is found early, when it is most treatable. Your child’s oncology team will outline which risks are relevant based on the specific treatment your child received.

A late-effects clinic — also called a cancer survivorship clinic — is a specialised follow-up service for childhood cancer survivors. It monitors for complications that can appear months or years after treatment ends, including second cancers, heart and lung effects of treatment, hormone and growth issues, and other organ-specific concerns. Most paediatric oncology guidelines recommend that survivors attend structured follow-up for at least five years after completing treatment, with many continuing into adulthood. At CION, our multi-disciplinary team provides personalised survivorship planning based on what each child received during treatment.

Yes. While the specific signs depend on what type of second cancer is being monitored for, general warning signs that a survivor or parent should promptly discuss with a doctor include: a new lump or swelling anywhere in the body; unexplained and persistent fatigue or pallor; unusual bruising or bleeding; persistent pain in any area, particularly bones; unexplained weight loss; and changes in skin over a previously irradiated area. These symptoms do not necessarily mean a second cancer is present — many have innocent explanations — but they should never be dismissed in a survivor who has received treatment. Scheduled follow-up visits are the most reliable safety net.