Chapter 4: Cancer incidence in Canada: trends and projections (1983-2032) – Hodgkin lymphoma - HPCDP: Volume 35, Supplement 1, Spring 2015

Chapter 4: Projections by Cancer Site

20. Hodgkin lymphoma

Hodgkin lymphoma (HL) is a relatively rare cancer. In 2003–2007, the average annual number of new HL cases was 490 for males and 395 for females, constituting 0.6% and 0.5% of all new male and female cancer cases in Canada, respectively (Tables 4.20.1 and 4.20.2).

HL is classified into 2 main groups: classical HL, the most common type, and nodular lymphocyte-predominant HL, which represents about 1 in 20 cases.^{Endnote 111, Endnote 267} The 5-year relative survival rates for HL diagnosed between 2006 and 2008 were 83% for males and 87% for females.^{Endnote 1}

HL has a bimodal age distribution, with peaks at age 20 to 24 and 75 to 79 for both sexes in 2003–2007 (Figure 4.20.1). The disease was more common in men than in women beginning in adulthood, although the rates corresponded at ages 10 to 19. Tables 4.20.1 and 4.20.2 show that more than 70% of all HL cases occurred in those younger than 55. The age distribution between males and females was nearly identical (Figure 4.20.1).

Figure 4.20.2 indicates that overall ASIR of HL decreased modestly in both sexes until 1998–2002. During 1998–2007, the ASIRs increased non-significantly in males by 0.4% per year and by 0.9% per year in females (Figures 3.1 and 3.2). Quebec, Ontario, the Atlantic region and the country had similar trends for males, British Columbia showed an opposite pattern from 1988–1992, and the rates in the Prairies seemed to stabilize (Figure 4.20.2). For females, the ASIRs in British Columbia and Quebec were similar to the entire country, and the rates in Ontario have decreased steadily since 1988–1992. The rates for females in the Prairies and the Atlantic region seem random, likely because of the small numbers of annual cases and the unusual age distribution of the cancer occurrence, making it complicated to interpret the trends.

The overall incidence rates for HL are projected to decrease slightly in both sexes (Figure 4.20.2), whereas the overall ASIRs are projected to increase steadily in the 45–54 age group and decrease or level off in other age groups (Figure 4.20.3). The ASIRs in males and females are predicted to converge in the age groups older than 54. Rates of HL in British Columbia males are projected to decrease significantly and diverge from those in other regions, where the rates will tend to remain unchanged and consistent (Figure 4.20.2). For females, the rates are projected to increase slightly in Quebec, the Atlantic region and the Prairies, and to decrease marginally in Ontario and British Columbia. The projected rates for HL in both sexes will be lowest in British Columbia and highest in Quebec.

From 2003–2007 to 2028–2032, the ASIRs of HL for Canada are expected to decrease by 3% in males, from 3.1 to 3.0 per 100 000, and by 7% in females, from 2.5 to 2.3 per 100 000 (Tables 4.20.3 and 4.20.4).

Due to the projected Canada population growth and aging, the annual number of newly diagnosed cases is predicted to increase by roughly 26% in both sexes, from 490 to 615 in males and from 395 to 500 in females (Tables 4.20.1 and 4.20.2).

Comments

The etiology of HL remains incompletely characterized. Known risk factors for HL include infectious agents, a compromised immune system, genetic factors, and social and environmental factors. EBV, a ubiquitous virus infecting 80% to 100% of people worldwide, plays a causative role in the etiology of the neoplasm.^{Endnote 52, Endnote 268, Endnote 269} The EBV genome is present in approximately 50% of the lymphoma cells of cases.^{Endnote 86} Patients with immunodeficiences or autoimmune diseases are at elevated risk of HL.^{Endnote 86} For instance, a systematic review shows an 11-fold increase in risk of HL in people with HIV/AIDS.^{Endnote 270} Familial aggregation of HL has been observed. Having a parent with the disease increases the risk 3-fold.^{Endnote 271} The familial risks are higher in males and in siblings.^{Endnote 271}

Recent reviews report that ever smoking is associated with a 10% to 15% increased risk of HL,^{Endnote 272, Endnote 273} functioning in a dose-dependent manner.^{Endnote 272} Socioeconomic status in childhood is also linked to the risk. High childhood socioeconomic status, single family housing, small family size and high maternal education increase HL risk.^{Endnote 274} It has been speculated that these social environments delay exposure to common infections which facilitate immune maturation.^{Endnote 274}

The bimodal age distribution of the incidence is expected to be the same in developed countries.^{Endnote 275} EBV is more commonly associated with HL cases in older adults or younger children, possibly suggesting an alternate age-dependent pathway. ^{Endnote 268} HIV plays a role in developing HL in young people.^{Endnote 275}