Second primary cancers in thyroid cancer patients: a multinational record linkage study

Area of Science:

• Oncology
• Epidemiology

Background:

• Rising thyroid cancer incidence and improved survival rates necessitate understanding secondary cancer risks.
• Thyroid cancer can occur as a second primary neoplasm following other cancer diagnoses.

Purpose of the Study:

• To evaluate the risk of developing a second primary cancer subsequent to a thyroid cancer diagnosis.
• To assess the risk of thyroid cancer as a second primary neoplasm following other initial cancers.

Main Methods:

• A multinational record linkage study involving 13 population-based cancer registries.
• Follow-up of 39,002 individuals with primary thyroid cancer for up to 25 years to identify second primary neoplasms (SPNs).
• Calculation of standardized incidence ratios (SIRs) by comparing observed SPN counts with expected numbers based on age-, sex-, and calendar period-specific incidence rates.

Main Results:

• A 30% increased risk (SIR 1.31) of any second primary cancer was observed after initial thyroid cancer.
• Significantly elevated risks were noted for numerous specific cancers following thyroid cancer.
• Increased risks of second primary thyroid cancer were also identified after various other primary cancer types.

Conclusions:

• Pooled data indicate a notable increase in second primary cancer risk after thyroid cancer and vice versa.
• While biases and chance may play a role, shared risk factors and treatment effects are likely implicated.
• Clinicians should maintain a high index of suspicion for second primary cancers in patients treated for thyroid cancer.