A second malignancy, unlike metastases from a pre-existing cancer, is a new primary cancer arising in a patient under treatment for another malignancy. This means that a patient suffering from and under treatment for a previously diagnosed primary cancer is subsequently diagnosed with another, different, cancer.
Though relatively uncommon, 20 per cent of the 25 million cancer survivors in the world are in the high risk zone to develop a secondary cancer either due to a genetic predisposition or previous treatment like chemotherapy and radiotherapy. Oncologists and cancer educationists have always emphasised that, while treating a cancer, the main focus should be on getting rid of the primary malignancy without worrying about secondary malignancies.
But due precautions and modifications of treatment plan are needed to reduce the possibility of second cancers in specific cases. Recent advances in cancer treatment, particularly in radiotherapy, have given treating oncologists a way to significantly reduce such risks.
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Children who develop primary cancers before the age of 15 are susceptible to second cancers because of the following reasons. One, they are often genetically predisposed to certain cancers. Two, childhood cancers have better cure rates and so the patients often live longer during which they can develop second cancers. Last, some chemotherapy and radiotherapy treatments for their first cancer make them more susceptible to second cancers.
Another group prone to second cancers are those having strong family history of cancers with a genetic predisposition to develop cancers, sometimes multiple. The phenomenon of field cancerisation — for example in aero-digestive tract cancers — often gives rise to a second cancer as the entire respiratory and upper digestive system is exposed to the same risk factors. Lifestyle choices, including smoking and uncontrolled obesity, often result in individuals getting multiple cancers.
Oncologists should consider the possibility of second cancers and discuss it with patients to help them make informed decisions, lifestyle modifications and participate in screening programmes if they are particularly susceptible. Every effort should also be made to minimise such risk from treatment of the primary cancer.
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An example is the reduction in the dose and volume of radiation treatment in Hodgkin’s Lymphoma over the last two decades. Technological advances like IMRT, IGRT, RapidArc and now FFF have significantly reduced radiation exposure to the surrounding normal tissues thereby reducing the risk of second cancers after patients are cured of their primary malignancy.