Worldwide, approximately 15% of cancer survivors are diagnosed with a second primary cancer. A study published in the Canadian Medical Association Journal (CMAJ) reveals that those who have survived cancer are at more than double the risk of a second primary cancer of the same type, but the risk of developing a second cancer of a different type is only marginally higher.
To establish whether the risk of secondary cancer is associated to the first diagnosed cancer, Danish researchers evaluated data for the entire Danish population (7,493,705 people) from 1980 to 2007. They established from a total of 843,118 diagnoses, that approximately 10% (765,255) had one or more diagnoses of primary cancer.
They discovered that cancer survivors had a 2.2-fold risk of developing a second primary cancer of the same type as the first and a 1.1 increased risk of developing a different type of second primary cancer.
They also noted that the risk varied, depending on the type of cancer, for example, the risk of a second cancer of the same type was reduced after prostate cancer, with the greatest reduction after sarcoma, whilst the risk of a second cancer of a different type was also reduced following prostate cancer with the greatest risk reduction after larynx cancer.
The researchers developed a table containing estimates of risks for recurrence and development of new cancers following 27 different types of cancers, to better understand the link between cancers, and suggest that their findings may prove valuable to further cancer investigations.
Dr. Stig Bojesen of Herlev Hospital, Copenhagen University Hospital and the University of Copenhagen, and his co-authors write:
“The striking contrast between the 2.2-fold increased risk of a second primary cancer being the same type as the first and the 1.1-fold increased risk of it being different from the first cancer suggests that characteristics of the individual patient were involved. The risk of a second primary cancer seems to be specific to cancer type and is probably driven by the patient’s genetic and lifestyle risk factors.”
They also investigated the link of the first cancer to smoking, as it is known that smoking increases the risks of many types of cancer.
Dr. Bojesen said:
“We were surprised to see that in our study, the risk of other smoking-related cancers in patients surviving a smoking-related cancer was only 1.2-fold. The good news is that in the individual cancer survivor, the increased risk of a new cancer is mainly confined to the same cancer as the first – even in people with an unhealthy lifestyle such as smoking.”
The authors write:
“We speculate that in general, risk factors acting over the long term seem to be type specific in the individual patient. However, other explanations are also plausible: effects of treatment and an increase (or decrease) in diagnostic surveillance could change observed risk of cancer in the same organ as opposed to other organs.”
They conclude:
“Future studies of individual pairs of first and second primary cancers should clarify whether the association is due to shared genetic or lifestyle risk factors, co-diagnosis of a primary cancer in close anatomic proximity to the first cancer, treatment of the first cancer or the timing of the diagnosis of the first cancer (in childhood v. adulthood).”
Dr. Marcy Winget from Alberta Health Services and her co-author comment writing in a related link, that:
“Nielsen and colleagues found that the risk of a second primary cancer depended greatly on the types of the first and second cancers; heterogeneity in risk was substantial across cancer types, regardless of whether the second cancer was the same type as the first.”
They highlight that this important heterogeneity needs to be examined first by risk for specific cancers that are paired and then second cancers, rather than overall risk.
They conclude writing, that:
“Caution must be exercised, however, in interpreting the findings for implications for clinical practice, in view of the substantial heterogeneity in risk.”
Written by Petra Rattue