Radiation exposure and familial aggregation of cancers as risk factors for colorectal cancer after radioiodine treatment for thyroid carcinoma.
OBJECTIVE
In thyroid cancer patients, radioiodine treatment has been shown to be associated with an increased risk of colon carcinoma. The aim of this study in thyroid cancer patients was to evaluate the role of familial factors in the risk of colorectal cancer and their potential interaction with radioiodine exposure.


METHODS
We performed a case-control study on 15 colorectal cancer patients and 76 matched control subjects, nested in a cohort of 3708 thyroid cancer patients treated between 1933 and 1998. For each patient, the radiation dose delivered to the colon by radioiodine was estimated by use of standard tables. In those who received external radiation therapy, the average radiation doses delivered to the colon and rectum were estimated by use of DOS_Eg software. A complete familial history was obtained by face-to-face interviews, and a familial index was defined to evaluate the degree of familial aggregation.


RESULTS
The risk of colorectal cancer increased with familial aggregation of colorectal cancer (p = 0.02). After adjustment for the radiation dose delivered to the colon and rectum, the risk of colorectal cancer was 2.8-fold higher (95% CI, 1.0-8.0) for patients with at least one relative affected by colorectal cancer than for patients without such a family history (p = 0.05). The radiation dose delivered to the colon and rectum by (131)I and external radiation therapy was associated with an increase of risk near the significance threshold (p = 0.1). No significant interaction was found between radiation dose and having an affected relative (p = 0.9).


CONCLUSIONS
The role of familial background in the risk of colorectal cancer following a differentiated thyroid carcinoma appears to increase with the radiation dose delivered to the colon and rectum. However, the study population was small and no interaction was found between these two factors.
National Institute of Public Health and Medical Research, INSERM, Unit 605, Institut Gustave-Roussy, 39 rue Camille Desmoulins, 94805 Villejuif, France.
Carole
C
Rubino
Elisabeth
E
Adjadj
Françoise
F
Doyon
Akhtar
A
Shamsaldin
Tahaa Moncef
TM
Abbas
Bernard
B
Caillou
Marc
M
Colonna
Claudia
C
Cecarreli
Claire
C
Schvartz
Stéphane
S
Bardet
Christiane
C
Langlois
Marcel
M
Ricard
Martin
M
Schlumberger
Florent
F
de Vathaire
D000465:Algorithms; D016022:Case-Control Studies; D003106:Colon / Q000528:radiation effects; D015179:Colorectal Neoplasms / Q000209:etiology* / Q000235:genetics; D005192:Family Health; D020022:Genetic Predisposition to Disease; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects*; D009381:Neoplasms, Radiation-Induced / Q000209:etiology* / Q000235:genetics; D011336:Probability; D012007:Rectum / Q000528:radiation effects; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000532:radiotherapy*
D007457:Iodine Radioisotopes