Cancer survivors have more than double the risk of getting a second primary cancer of the same type as individuals who have not experienced cancer, reports a Danish study in the Canadian Medical Association Journal (CMAJ).

Overall patients surviving certain types of cancer are known to be at increased risk of a second primary cancer. However, it has been unclear whether this excess risk was due to the second primary cancer being the same type as the first cancer, or being of a different type.

In the study Stig Bojesen of Herlev Hospital, Copenhagen University Hospital and the University of Copenhagen, and colleagues, examined three bases covering the entire population of Denmark (7.5 million people ) between 1980 and 2007 to determine whether the risk of secondary cancer is linked to the type of cancer found in the first instance.

Altogether 765,255 people had one or more diagnoses of primary cancer, with a total of 843,118 diagnoses.

In the 25 years of follow-up the investigators found a 2.2-fold risk of a second primary cancer of the same type as the first in cancer survivors; while the risk of a different type of second primary cancer was 1.1-fold.

Risk varied depending on the type of cancer, with the risk of a second cancer of the same type being reduced after prostate cancer, and showing the greatest reduction after sarcoma.

"Thus, 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," write the authors.

The researchers developed a table containing estimates of risks for recurrence and development of new cancers for 27 different types of cancers.

"Our present findings may assist clinicians in designing surveillance

programs for their patients who have cancer, for example by focusing on second primary cancers with the highest five-year absolute risks," write the authors.

Reference

S Nielsen, B Nordestgaard, S Bojesen. Associations between first and second primary cancers: a population-based study. CMAJ November 28, 2011, doi:10.1503/cmaj.110167