The purpose of this study is to compare the incidence rate of leukemia between CT-exposed and CT-unexposed group in patients who underwent appendectomy in South Korea.

South Korea has a single-payer healthcare system, administered by National Health Insurance Service (NHIS). As healthcare providers in South Korea need to claim reimbursement to NHIS for the vast majority of diagnostic and therapeutic procedures, the NHIS database enabled us to construct a large cohort who did or did not undergo CT for appendicitis. The purpose of this study is to compare the incidence rate of cancer between CT-exposed and CT-unexposed group in patients who underwent appendectomy in South Korea.

Inclusion Criteria:

• Patients will be entered in the cohort on the date of appendectomy under the diagnosis of appendicitis

Exclusion Criteria:

• (a) patients who had a cancer diagnosis before the date of appendectomy,
• (b) those who had prior experience of CT examination more than 7 days before appendectomy,
• (c) those who had syndromes or diseases predisposing cancers,
• (d) those whose diagnosis was changed to appendiceal cancer and
• (e) those whose follow-up duration was shorter than a lag period.

Patients who underwent appendectomy under the diagnosis of appendicitis