All cancers154118231980

year-olds was more than three times that seen in 13- to 14-year-olds.

In contrast to ALL, rates for NHL increased with increasing age. Only about half of all registered cases were coded to a specific subtype of NHL. The subtypes specified in the dataset are inconsistent with the current international classification of lymphomas, since the classification of NHL has changed substantially during the period covered [20, 21]. However, in summary, nearly 80% of all cases with a specified subtype across the age range 13 to 24 years were classified as diffuse, about 10% as follicular/nodular, and the remainder as other miscellaneous subtypes. The incidence of Hodgkin lymphoma increased markedly with age, and the incidence among 20- to 24-year-olds was more than three times that seen in 13- to 14-year-olds. HD subclassification was consistent across the time period and was based on the Rye Conference scheme [22]. More than two-thirds of the Hodgkin lymphoma cases were coded to a specified subtype. Of these, more than 70% were nodular sclerosing Hodgkin lymphoma, and this proportion did not differ markedly within age groups. Mixed cellularity Hodgkin lymphoma comprised nearly 20% of all specified cases and was somewhat more frequent among 15- to 24-year-olds than in 13- to 14-year-olds. Lymphocyte-predominant Hodg-

kin lymphoma formed less than 10% of all specified cases but was rather more frequent at younger than older ages. Lymphocyte-depleted HD was infrequent across all age groups.

Table 3.5 presents incidence rates of malignant CNS tumors. The most frequent CNS tumor was astro-cytoma, and in those with a specified subtype, low-grade astrocytomas were more common than glioblastoma and anaplastic astrocytoma in the 13- to 14-year-olds and 15- to 19-year-olds. However, the difference in rates between low-grade and high-grade astrocytoma was less marked in 15- to 19-year-olds than in the younger age group. In 20- to 24-year-olds, high-grade astrocytomas were more frequent than low-grade variants. Rates for ependymoma did not differ markedly among the age groups, but epen-dymoma was somewhat more frequent in the youngest group. Medulloblastoma and other primitive neuro-ectodermal tumors (PNETs) were twice as common in the younger age group as in patients aged 15-24 years. The rates for CNS tumors overall did not differ greatly across age groups. Although rates were only slightly higher in 13- to 14-year-olds than in 20- to 24-year-olds, they constituted 18% of all cases in the younger age group, but less than 8% in the older group (Table 3.2).

Table 3.6 presents the incidence of bone tumors and STS. Rates for bone tumors were higher among patients aged 13 to 19 years than among 20- to 24-year-olds. In all three age groups, osteosarcoma was the most frequent tumor, but the proportion of osteosarcoma was lower in 20- to 24-year-olds, with a relatively higher proportion of chondrosarcoma compared with the younger age groups. Ewing tumor is the second most common type of bone tumor in all three age groups, but rates are higher in 13- to 14-year-olds than at older ages, and the rate in the 20- to 24-year-olds is only half that seen in the youngest group.

STS, although less common than bone tumors, constitute an important group of malignancies in adolescents and young adults. STS represent about 6% of all malignancies in 13- to 14-year-olds. Rates for rhabdomyosarcoma are lower in the 20- to 24-year-olds, but rates for other STS increase with age.

Table 3.7 reports incidence rates for carcinomas. In 13- to 14-year-olds and 15- to 19-year-olds, the head and neck forms the most common primary site group for carcinomas, making up 46% and 41%, respectively, of all carcinomas among these two age groups, but in 20- to 24-year-olds, carcinomas of the head and neck region make up only 25% of all carcinomas. The thyroid is by far the most common primary site for carcinomas in the head and neck, and rates for carcinoma of the thyroid steadily increase across the three age groups. Nasopharyngeal carcinoma (NPC), which is extremely rare in the population in Britain in general, [19] makes up more than 10% of all carcinomas in 13-to 14-year-olds, but represents only 2% among 20- to 24-year-olds, although the rate is similar to that seen in the younger age group.

Carcinomas of the lung, breast, colon, rectum, and bladder constitute nearly 50% of all cancers at all ages [19], but are all uncommon in adolescents and young adults. However, examples of all of these carcinomas are seen, and the rates increase from the 13- to 14-year age group to the 20- to 24-year-olds. The rates for carcinomas of the genitourinary tract show a marked increase across the three age groups. Genitourinary tract carcinomas comprise 18% of all carcinomas in 13- to 14-year olds, but 21% and 42% in the 15- to 19-year-olds and 20- to 24-year-olds, respectively. All sites within the genitourinary tract show increases with age, but the greatest increases are for invasive carcinoma of the cervix and uterus. The most common sites among carcinomas of the gastrointestinal tract are the colon and rectum in all three age groups. Adrenocortical carcinoma is rare, but is seen across the 13- to 24-year age range.

Table 3.8 includes incidence rates for germ cell tumors, melanoma, and certain tumors that are seen typically in younger children. The most dramatic increase in rates with age among the adolescent and young adult group occurs in the gonadal germ cell tumors, for which the rate increases from 0.33 per 100,000 in 13- to 14-year-olds to 1.25 in 15- to 19-year-olds, and to 3.76 in 20- to 24-year-olds, representing more than an 11-fold increase in rates over the age range. This is entirely due to testicular germ cell tumors. Nongonadal germ cell tumors are much less frequent than gonadal, and although rates increase across the age groups, the trends with age are less dramatic. There is a small decrease in rates with increasing age for intracranial germ cell tumors. Wilms tumor, neuroblastoma, hepatoblastoma, and retinoblastoma have peak incidences in children aged less than 5 years, but a small number of cases have been registered in the adolescent and young adult age range. Cases of pan-creatoblastoma and pulmonary blastoma are also present. Collective rates for all of these tumors are shown in the table as "other embryonal tumors NEC." In addition, it is interesting to note that there are several cases of myeloma, which normally occurs in much older patients.

There are also marked differences in the incidences of certain cancers in this age group by gender, ethnicity, and country that are described in more detail elsewhere [23, 24]. Ethnic/racial differences in incidence are particularly apparent between African-American and non-Hispanic white adolescents and young adults. For example, among 15 to 19-year-olds in the United States, the overall incidence of cancer is 50% higher among whites than among blacks. The incidences of specific cancers such as melanoma and Ewing sarcoma are strikingly higher among whites, as is the case for all age groups. ALL, germ cell tumors, and thyroid cancer are also more common among whites than blacks, each by at least twofold. Among the common cancers in this age group, only STS, considered as a group, are more common among blacks than whites. Internationally, the incidence of melanoma varies the most among members of this age group [25], with rates in adolescents up to five times higher in Australia, where the incidence of melanoma is the highest in the world among both adults and children [3, 10].

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