TORONTO - Some patients who undergo successful treatment to beat Hodgkin's lymphoma may not be able to close the book on cancer for good, say researchers, who found that survivors of the disease have a higher than normal risk for a second type of malignancy later in life.
In a collaborative study, Canadian, U.S. and European researchers evaluated the risks of developing a second cancer up to 30 years after diagnosis with Hodgkin's lymphoma (HL), a disease of younger people that affects the lymphatic system.
They found that the incidence of all types of solid-tumour cancers, except bladder and prostate, was elevated compared to the general population.
"What we saw in these survivors was that in their mid-30s or even younger that they had risks of breast and colorectal cancer that were comparable to an average 50-year-old," said lead author Dr. David Hodgson, a radiation oncologist at Princess Margaret Hospital in Toronto.
For instance, women aged 40 or older who had been diagnosed with Hodgkin's at 30 had a six-fold higher chance of developing breast cancer, the study found. The risks for other forms of cancer were also increased (up to 20-fold for the rarest forms) and none declined until about age 70, when they were still above expected levels.
"We estimated that almost 25 per cent of women diagnosed with HL at age 20 would develop a second cancer by age 50," Hodgson said. Among the general population, the expected cancer risk is less than five per cent at that age.
An estimated 850 Canadians are diagnosed with Hodgkin's lymphoma each year and more than 100 die of the disease. The average age of diagnosis is 30, although it can also affect adolescents. The good news is that five-year survival rates after treatment are 80 to 90 per cent.
Ironically, it is the very treatment that cures the lymphoma that appears to beget the second type of cancer down the road, said Hodgson, and that's particularly true for patients in the study, most of whom were treated in the 1970s and '80s.
During that period, doctors used much higher doses of radiation compared with today and treatment often targeted lymph nodes in multiple sites on the body, including the neck, chest and abdomen - places where second tumours often arise.
Chemotherapy decades ago also was less refined. In fact, doctors later found that two of the commonly used drugs in the chemo cocktail of the '60s and '70s were associated with the development of a second cancer.
Today, "we're using a different chemotherapy recipe, and it carries with it a considerably lower risk of developing a second cancer," said Dr. Joe Connors, chair of the Lymphoma Tumour Group at the B.C. Cancer Agency.
Commenting on the study, in which he was not involved, Connors said doctors have long known that patients treated for HL are at greater risk of a subsequent cancer, but this research builds on and refines those previous observations.
"Fortunately, most people who have Hodgkin's lymphoma cured won't develop a second cancer . . . but a small percentage of them will," Connors said from Vancouver, noting that the study helps doctors recognize which cancers those might be, so they can caution patients against certain compounding behaviours, like smoking.
Such studies also alert physicians to think about tests for early detection of second cancers, "such as mammography to detect breast cancer or screening of a person's skin to detect melanoma," he said. "We can do these things to increase the likelihood that if they do develop a cancer, we'll pick it up early."
The research, published online Monday in the Journal of Clinical Oncology, analyzed patient data from population-based cancer registries across Europe and North America. The investigators identified 18,862 five-year survivors of Hodgkin's lymphoma and looked at the risk of second cancers over time. The data included patients treated up to 30 years earlier.
Hodgson said he and his fellow researchers, which included the principal investigator from the U.S. National Institutes of Health, teased out 1,490 patients who had developed a second cancer, 850 of them "above and beyond what would be expected" at their age.
The study focused in particular on breast and colorectal cancers because screening programs exist that could help detect these malignancies at an early stage. In Canada, screening for breast and colorectal cancers is recommended for most people starting at age 50.
"So I'd say for the long-term survivors, patients that are more than five years off their treatment, they need to be aware of these risks," Hodgson said. "Health-care providers also need to be aware of this because it should probably influence how they would investigate new symptoms, like a new persistent cough or change in bowel habit if it was a long-term HL survivor compared to their patients in a general practice."
"And so with the cure rates being so good and the patients being so young, they potentially have a long life ahead of them where we need to be concerned about their long-term health."
Still, both Hodgson and Connors stressed that the research findings shouldn't scare anyone diagnosed with Hodgkin's lymphoma away from treatment.
"The way I characterize it to my patients . . . is if we don't cure that disease then everybody dies of it," said Connors. "So the greatest risk to a person is that we would not as fully as we can effectively treat their Hodgkin's lymphoma."
"That's 'the' most important need that they have once they have the disease."
