Temporal trends and clinical correlates for the ret/PTC1 mutation in papillary thyroid carcinoma.

BACKGROUND

The incidence of papillary thyroid carcinoma (PTC) has increased in Australia at a rate exceeding 10% per annum over the past two decades. In Tasmania the increase has averaged 24% per year between 1982 and 1997. Exposure to ionizing radiation is the best characterized risk factor for PTC. Oncogenic mutations of the RET proto-oncogene (ret/PTC rearrangements) have been associated with PTC arising following radiation exposure. In the present study it was sought to determine if PTC incidence trends were associated with an increased occurrence of the ret/PTC1 rearrangement.

METHODS

All cases of PTC diagnosed in Tasmania during the even numbered years 1978-1998 inclusive were sought for study (n = 98). Archival histopathology blocks for 62 cases were located. The RNA was successfully extracted from 41 tumours and ret/PTC1 status assessed by reverse transcription-polymerase chain reaction.

RESULTS

The ret/PTC1 mutation was found in 26 (63%) of PTC. The mean age at diagnosis for ret/PTC1-positive and ret/PTC1-negative tumours was 46.5 +/- 15.46 and 41.9 +/- 13.45 years, respectively. The ret/PTC1 positivity was significantly associated with larger tumour size. However, ret/PTC1 was not associated with an adverse prognosis. The prevalence of tumours positive for ret/PTC1 remained stable over the study period (1978-1998) and did not exhibit birth year or diagnosis year clustering.

CONCLUSION

This is the first study to map temporal trends for the prevalence of ret/PTC1 relative to incidence trends for PTC. Although the ret/PTC1 mutation was frequently identified in Tasmanian PTC, there was no clear relationship between ret/PTC1 and recent PTC incidence trends.