Population-based study of familial medullary thyroid cancer.

BACKGROUND

We wanted to carry out a population-based study on medullary thyroid cancer (MTC) in order to quantify familial risks.

METHODS

MTC was studied in the Swedish Family-Cancer Database, updated in 1999 to cover individuals and offspring, born after 1934 with their biological parents, totaling 9.6 million persons. Cancer data were obtained from the Swedish Cancer Registry from year 1958 to 1996 and included 2,435 thyroid cancers among offspring.

RESULTS

65 offspring were identified with MTC, which was coded as a separate entity since 1985. 62% had neither affected parent nor sib. Most familial cases were diagnosed at ages 15 to 24 and sporadic cases 25 years later. The familial SIRs of MTC were 3,080 and 3,650 when either a parent or a sib had MTC; when both had MTC the SIR was 35,800. All the familial risks were highest in young age groups, 0-9 years. MEN 2 or MEN 2-like families were considered when one family member had a TC and an adrenal pheochromocytoma. SIR of MTC in offspring was 61,000 when a parent had a MEN 2-like cancer and a sib had MTC.

CONCLUSIONS

We described familial and sporadic MTC in a population-based database. The familial risks of MTC may be the highest ever reported in population based studies.