2017 Section 7 Green Book

Surgery June 2012

Lang et al

DTC, particularly for low-risk tumors, has been in- creasingly advocated. 18 Although I 131 is preferen- tially taken up by the normal and malignant thyroid follicular cells, particularly under the hypo- thyroid state, it is also taken up and accumulated into the stomach, salivary glands, colon, and blad- ders; these sites are often exposed to prolonged ra- diation. Interestingly, these sites were reported to the common sites for NSPM in DTC survivors. 5,15 In the present study, because only 2 female patients belonging to the RAI + group developed stomach and bladder cancers during the study period (data not shown), respectively, it was difficult to know whether these tumors were actually related to RAI therapy or occurred by chance. Calculating the SIR value for these 2 primary tumors was also not possible. Nevertheless, similar to previous studies, we did find that breast cancer was one of the most common NSPMs in DTC survivors. In addition, the relative frequency of the 3 most common NSPMs (ie, breast, colon, and lung) observed in the present study appeared similar to the frequency observed in other population studies. 5,6 Their fre- quencies ranged between 0.1% and 0.2% per 1 person-year of observation. 6 Possible explanations Table III. Cox proportional hazards analysis of factors for the development of nonsynchronous second primary malignancy in differentiated thy- roid carcinoma Covariates Relative risk 95% CI P value Age of DTC by groups, y < 30 Reference 30–49 1.468 0.690–3.121 .319 $ 50 1.704 0.910–5.085 .263 Sex Female Reference Male 1.299 0.695–2.430 .413 Period of DTC diagnosis Before 1980 Reference 1980–1999 1.676 0.840–3.346 .143 After 2000 1.717 0.601–4.910 .313 Cumulative RAI activity, GBq None Reference 3–8.9 2.777 1.079–7.145 .034 > 9.0 3.149 0.645–12.816 .131 Stage of DTC by TNM I Reference II 1.678 0.764–3.627 .162 III 1.513 0.681–3.364 .309 IV 1.760 0.781–3.969 .173 CI , Confidence interval; DTC , differentiated thyroid carcinoma; NSPM , nonsynchronous second primary malignancy; RAI , radioactive iodine (I 131 ); TNM , American Joint Cancer Committee/Union Internationale Contre le Cancer tumor-nodes-metastasis staging system, 6th edition.

and sex, the incidence or risk of developing NSPM in RAI + group was significantly higher, but in the RAI group, the incidence or risk appeared not sig- nificantly different to the general population. In the RAI + group, for both sexes, the SIR was 1.51 (95% CI, 1.14–1.96). For males in the RAI + group, the SIR was 1.41 (95% CI, 0.77–2.37), and for fe- males the SIR was 1.54 (95% CI, 1.11–2.02). In con- trast, for males in the RAI group, the SIR was 0.53 (95% CI, 0.01–2.96), and for females the SIR was 0.92 (95% CI, 0.37–1.90). DISCUSSION Previous studies found that the overall lifetime risk of developing NSPM was higher in DTC survi- vors by up to 30% to 40% more than that of the general population. 4,14 The present study, unlike our previous studies, was aimed at specifically evalu- ating whether RAI therapy was a potential risk factor for NSPM in a cohort of radiation-na € ıve DTC survi- vors. 4,15 Other proposed risk factors included expo- sure of ionizing radiation during DTC treatment, common environmental and dietary factors, ge- netic predisposition, and surveillance bias. 5,8 How- ever, ionizing radiation exposure from treatment of DTC remains one of the most likely culprits for NSPM because RAI therapy is commonly admin- istered in DTC either in the setting of thyroid rem- nant ablation after total or near-total thyroidectomy or in the setting of recurrence or metastasis. 5,6,16,17 As a result, more selective use of RAI therapy in Figure. The cumulative risk curves of developing non- synchronous second primary malignancy (NSPM) after the diagnosis of differentiated thyroid carcinoma (DTC) in those who received radioiodine therapy (RAI + group) and those who received no radioiodine therapy (RAI group).

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