Incidence of Second Malignancies Among Children Treated for Cancer With Radiotherapy in Egypt

Survivors of childhood cancer (CCS) are at risk for secondary malignant neoplasms (SMNs): serious late effects of treatment. Radiotherapy (RT) and chemotherapy (CT) are possible causes of SMNs.

To measure SMN incidence and characteristics among Egyptian CCS treated with RT, and to compare SMN timing and location based on RT field and CT type.

We performed a retrospective cohort study of patients under 18 years who received radiotherapy for primary cancer at the Children's Cancer Hospital, Cairo, Egypt, from 2009 to 2015, with follow-up through 2021. We calculated cumulative incidence functions for second malignant neoplasm (SMN) development overall and by primary diagnosis, using the Fine and Gray method, both for all SMNs and for in-field SMNs. We used the Wilcoxon rank-sum test to compare time to SMN between patients with in-field versus out-of-field SMNs and those who received alkylating versus non-alkylating chemotherapy. Of 3132 patients (60.1% male; median age 6.2 years), 23 developed an SMN (11.1-year cumulative incidence: 1.85%, 95% CI: 0.84%-3.57%). Eight (34.8%) of the 23 SMNs arose within the prior RT field (11-year cumulative incidence: 2.71%, 95% CI: 1.32%-4.93%). Median time to SMN was longer for in-field than out-of-field cases (7.9, IQR: 6.0-9.9 vs. 4.3 years, IQR: 2.7-5.6; p = 0.002). There was no significant difference in time to SMN by CT type.

SMN incidence in this cohort matched rates in high-income countries. Strong long-term follow-up is essential for CCS in Egypt and similar settings.