Summary: multiple primary cancers in Denmark, 1943-80

Area of Science:

• Oncology
• Epidemiology
• Cancer Research

Background:

• Understanding the risk of second primary cancers is crucial for cancer patient management.
• Previous studies have yielded varying results on cancer patient susceptibility to new malignancies.

Purpose of the Study:

• To investigate the risk of developing a second primary cancer among a large cohort of Danish cancer patients.
• To identify factors influencing second primary cancer development, including time since diagnosis, age, and potential common etiologies.

Main Methods:

• Analysis of 171,749 men and 208,192 women diagnosed with cancer between 1943 and 1980 in the Danish Cancer Registry.
• Inclusion of patients surviving at least 2 months, accumulating over 1.7 million person-years of observation.
• Calculation of relative risks (RR) for second primary cancers, with adjustments for underreporting.

Main Results:

• The overall RR for a second primary cancer at a different site was 0.99 (adjusted to 1.06).
• RR increased with time, from 0.94 in the first decade to 1.13 at 30 years.
• Elevated risks observed for common etiology sites (e.g., smoking-related cancers) and specific treatment exposures (e.g., radiotherapy and subsequent cancers).
• Patients diagnosed before age 20 had a significantly increased risk of second cancers.

Conclusions:

• Cancer patients generally do not exhibit a heightened susceptibility to new malignant tumors.
• Specific risk factors, such as shared etiologies and cancer treatments, can increase the likelihood of developing a second primary cancer.
• The study highlights the importance of long-term surveillance for cancer survivors, particularly those treated with radiotherapy or diagnosed at a young age.