Pattern of cancers in adolescent and young adults.

Discussion

The data on the pattern of cancers in the AYAs is scant in Saudi Arabia, rather an extensive search of literature revealed no published reports on the cancer in this strategically important age group from Saudi Arabia.⁸ However, an expanding knowledge of cancers in AYAs is available from many countries such as United States,^3,9 Europe,⁴ Canada,⁵ Australia,¹⁰ the Netherlands,¹¹ Korea,¹² Lebanon,¹³ Brazil,¹⁴ India,² and Japan.¹⁵ The recent advances in the coordinated international research and newer treatment modalities in the pediatric cancer have led a remarkable improvement in the outcomes. However, cancers in AYAs have not benefited from similar efforts and this deficit has led the international researchers to focus more on this strategically important age group.⁹ The World Health Organization (WHO) has defined adolescent period from 10-19 years and youth as those with age from 15-24 years, while, the United States Surveillance Epidemiology and End Results (SEER) program have defined the AYAs as those aged between 15-39 year^3,9 but, many other internationally recognized societies have define the AYAs population ranging in a range from 15-29 years.^5,11-14 For better understanding of the cancers in AYAs we kept the age range from 15-29 years in our cohort.

Although, the present study was a retrospective and a single hospital-based research, yet, it can serve the purpose of providing the trends of AYAs with their basic demographic correlations which can be compared with the available research in the English literature. During the period of 15 years, a total of 475 cases of various cancers were reported in the AYAs which constitute 5.4% of total number of cancers diagnosed at KFH. The rate of cancer in AYAs in our cohort is higher than the reported number from Korea (2.3%),¹² Lebanon (2.9%),¹³ and Japan (3%).¹⁵ Sharma and Singh² from India reported 5.7% of cancers in AYAs which corresponds with our finding. Of these 475 cases, 232 (48.8%) were males while 243 (51.2%) were females, with a male-to-female ratio of 0.9:1, indicating a slight female preponderance. The female preponderance in our study corresponds to those of previous studies conducted in the United States of America,⁹ Netherlands,¹¹ Korea,¹² and Lebanon.¹³ The female predominance was mainly attributed to the higher incidence of thyroid and breast carcinomas in these studies, similar observation was made in our study as well. Contrary to our observation of female preponderance, there are few studies from India reported a higher incidence of cancers in male AYAs. This higher incidence in male is mainly attributed to the male preference in India and some cancers such as lymphoma and leukemia are more common in males in their cohort.²

In this study, we divided the cancers in AYAs in 3 different age groups. As the international classification of childhood cancer is not appropriate for AYAs, Birch et al⁷ in 2002 proposed a new classification for this age group in accordance with the WHO for AYA and according to the International Classification of Diseases for Oncology (ICD-O). We also classified our observation of cancers in AYAs according to Birch classification and ICD-O.⁷

In our study, the most encountered individual cancer was lymphoma, which was observed in 28.4% (135/475) of cases for both gender and with not much differences between the different analyzed age groups. Barmant et al¹⁴ from Brazil and Scott et al⁹ from the USA in their study also reported similar finding of lymphoma being the frequently diagnosed cancer in AYAs. An interesting observation was noted in our study regarding the occurrence of various cancers in the different age group, we observed that AYAs age increased in the total number of cancers (Figure 1). There is an obvious difference in the type of cancers in young AYAs than the older AYAs. While lymphomas and leukemias were the most common cancers in the young AYAs, various epithelial carcinomas especially thyroid and breast carcinomas were more common in the older AYAS. This is mainly due to an increase in the occurrence of carcinoma in the older AYAs. The increased occurrence in carcinoma was primarily due to an increase rate of thyroid and breast carcinoma in the older AYAs, similar observations were noted in the United States,⁹ the Netherlands,¹¹ Korea,¹² and Brazil.¹⁴ It is primarily attributed to a rapid increase in the incidence of these malignancies in the older population and partially due to increase awareness and easy availability of screening tests and diagnostic facilities. However, the exact cause for the increased incidence of other cancers in AYAs is still unknown.^9,12 We also observed that there is a decreasing trend in the relative incidence of leukemias, lymphomas, CNS tumors, bone, and soft tissue sarcomas and relative increase in the carcinomas as the age increases in the AYAs. Similar observations were reported by previous authors.^9-11 This shift may be attributed to many factors including hormone levels during puberty and pregnancy and exposure to environmental factors (late onset) versus genetic factors (early onset).⁹ Another contrasting finding in our study was the incidence of melanoma which is lesser as compared to studies carried out in the US SEER³ Australia,¹⁰ and the Netherlands.¹¹ This could be attributed to chronic continuous sun exposure and increased melanin pigmentation in the majority of our people which acts as a natural sun protection factor. A detailed comparison of our findings of cancers in AYAs with the previously published literature is summarized in Table 2.