In
adults, the majority of cancers are carcinomas, which arise in the
epithelium of the colon, breast, lung, bladder, and skin. In children,
carcinomas are rare, and the spectrum of disease is quite different
to that in adults. In Canada from 2000 to 2004, leukemias accounted
for around 33% of childhood malignancies, brain and other
central nervous system tumors for 20%, lymphoma for 12%, neuroblastoma
for 7%, soft tissue for 6%, renal tumors for 5%,
bone tumors for 4%, and the remaining 13% represented
a collection of very rare tumors (Fig. 444-1).2 The
distribution is similar in other geographic areas.3,4 Over
the course of childhood, the types of cancers change: In infants,
the most common form of cancer is neuroblastoma (25% of cancer
diagnoses) and for 1- to 14-year-olds, the most common is leukemia
(42% of cases, ages 1–4; 34% of cases,
ages 5–9; and 22% of cases ages 10–14; eFig. 444.1).2 The outcome
for children with cancer varies with the type of disease, as discussed
below. Overall, the rate of cancer is about 20% higher
in boys than in girls, with the difference being most marked for
lymphomas, which are twice as common in boys (eFig.
444.2).2