Cancer Incidence and Mortality in Patients Treated Either With RAI or Thyroidectomy for Hyperthyroidism.
BACKGROUND
Some previous studies have suggested increased cancer risk in hyperthyroid patients treated with radioactive iodine (RAI). It is unclear whether the excess cancer risk is attributable to hyperthyroidism, its treatment, or the shared risk factors of the two diseases.


OBJECTIVE
The objective was to assess cancer morbidity and mortality in hyperthyroid patients treated with either RAI or surgery.


METHODS
We identified 4334 patients treated surgically for hyperthyroidism in Finland during 1986-2007 from the Hospital Discharge Registry and 1814 patients treated with RAI for hyperthyroidism at Tampere University Hospital. For each patient, three age- and gender-matched controls were chosen. Information on cancer diagnoses was obtained from the Cancer Registry. The follow-up began 3 months after the treatment and ended at cancer diagnosis, death, emigration, or the common closing date (December 31, 2009).


RESULTS
The overall cancer incidence was not increased among the hyperthyroid patients compared to their controls (rate ratio [RR], 1.05; 95% confidence interval [CI], 0.96-1.15). However, the risk of cancers of the respiratory tract (RR, 1.46; 95% CI, 1.05-2.02) and the stomach (RR, 1.64; 95% CI, 1.01-2.68) was increased among the patients. The overall cancer mortality did not differ between the patients and the controls (RR, 1.08; 95% CI, 0.94-1.25). The type of treatment did not affect the overall risk of cancer (hazard ratio for RAI vs thyroidectomy, 1.03; 95% CI, 0.86-1.23) or cancer mortality (hazard ratio, 1.04; 95% CI, 0.91-1.21).


CONCLUSIONS
In this cohort of Finnish patients with hyperthyroidism treated with thyroidectomy or RAI, the overall risk of cancer was not increased, although an increased risk of gastric and respiratory tract cancers was seen in hyperthyroid patients. Based on this large-scale, long-term follow-up study, the increased cancer risk in hyperthyroid patients is attributable to hyperthyroidism and shared risk factors, not the treatment modality.
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Essi
E
Ryödi
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Saara
S
Metso
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Pia
P
Jaatinen
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Heini
H
Huhtala
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Rauni
R
Saaristo
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Matti
M
Välimäki
Heart Center Co. (R.E.), Tampere University Hospital, 33521 Tampere, Finland; School of Medicine (R.E., M.S., J.P.), University of Tampere, 33521 Tampere, Finland; Department of Internal Medicine (M.S., J.P.), Tampere University Hospital, 33521 Tampere, Finland; Department of Internal Medicine (J.P.), Seinäjoki Central Hospital, 60220 Seinäjoki, Finland; School of Health Sciences (H.H., A.A.) and Department of Surgery (S.R.), Tampere University Hospital, 33521 Tampere, Finland; and Division of Endocrinology (V.M.), Department of Medicine, Helsinki University Central Hospital, 00100 Helsinki, Finland.
Anssi
A
Auvinen
D000328:Adult; D000368:Aged; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D006980:Hyperthyroidism / Q000532:radiotherapy / Q000601:surgery / Q000628:therapy*; D015994:Incidence; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000401:mortality; D012042:Registries; D012307:Risk Factors; D013965:Thyroidectomy / Q000009:adverse effects*
D007457:Iodine Radioisotopes