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

Chapter 4: Projections by Cancer Site

21. Non-Hodgkin lymphoma

In 2003–2007, non-Hodgkin lymphoma (NHL) was the fifth most common type of new cancer diagnosis in Canadian males and females, and the most common lymphohematopoietic cancer. The average annual number of newly diagnosed NHL cases in this period was 3455 for males and 2915 for females, representing 4.3% and 3.9% of all new male and female cancer cases, respectively (Tables 4.21.1 and 4.21.2).

The lifetime risk for developing NHL is 2.4% in males and 1.9% in females.Endnote 1 NHL was the second most common (9.4%) incident cancer in males younger than 45 in 2003–2007 (Figure 3.9). The ASIRs of NHL increased with age to 122.0 per 100 000 in men aged 85 and over and to a maximum of 81.7 per 100 000 in women aged 75 to 84; the increase was less pronounced in women than in men (Tables 4.21.3 and 4.21.4).

Overall, NHL occurred nearly 1.5 times as often in males as in females. More than 70% of all incident NHL cases occurred in people aged 55 or older (Tables 4.21.1 and 4.20.2). NHL has an intermediate 5-year relative survival rate among all cancers in Canada, at 65% in males and 69% in females for 2006–2008.^{Endnote 1}

Figure 4.21.1 indicates that overall incidence rates increased modestly in both sexes during the entire observation period. During 1998–2007, the ASIRs for NHL increased significantly in males by 0.8% per year and increased non-significantly in females by 0.5% (Figures 3.1 and 3.2).

Figure 4.21.2 reveals that the incidence of NHL increased over the observation periods for age groups above 55 in both sexes. For age groups below 55, the rates increased to their peaks in 1993–1997 for men under 45 and women aged 45 to 54, and in 1998–2002 for the opposite age–sex combinations, and then rates decreased.

The incidence rates of NHL in males are predicted to peak (at 19.9 per 100 000) in 2008–2012 and then decrease slightly, while the rates in females will peak in 2013–2017 and then level off (Figure 4.21.1). The projected flat trajectory of the rates might be because of a decrease in rates in later birth cohorts, especially in males.

Even though the rates were very similar for all regions in the most recent 2 to 3 observed periods, the rates in the Atlantic region are predicted to diverge slightly in the future in females. The Atlantic region had the most marked increase, and these rates are projected to stabilize. The rates in the other regions are expected to be consistent, changing marginally with the same pattern as for the country.

Figure 4.21.2 shows that the ASIRs in males and females are projected to converge in age groups under 75 and to diverge in older age groups.

From 2003–2007 to 2028–2032, the ASIRs for NHL in Canada are projected to decrease by 8% in males, from 19.7 to 18.1 per 100 000, and to remain relatively stable in females, from 14.1 to 14.3 per 100 000 (Tables 4.21.3 and 4.21.4). The annual number of new male cases is estimated to increase by 75%, from 3455 to 6050, and the annual number of new female cases, by 78%, from 2915 to 5180 (Tables 4.21.1 and 4.21.2).

Comments

The observed incidence patterns likely result from a combination of improved detection and classification of this complex set of diseases, as well as changes in suspected risk factors because most of the risks for NHL are unknown.^{Endnote 36} Familial aggregations of NHL have been observed.^{Endnote 276, Endnote 277} Immunodeficiency is one of the best characterized and strongest known risk factors for NHL. Risk is increased whether the immunodeficiency is congenital, iatrogenic or acquired.^{Endnote 278} NHL is over 50 times more common in patients with congenital or acquired immunodeficiency than in the general population.^{Endnote 278} The increase in the prevalence of acquired immunodeficiency syndrome (AIDS) in the 1980s is responsible in part for increased incidence rates during that period.

Infectious agents of human T-cell lymphotropic virus type 1 (HTLV-1), EBV and HCV have also been associated with an increased risk of NHL.^{Endnote 47} A number of studies have pointed to a positive association between HCV infection and NHL,^{Endnote 279, Endnote 280} but a causal relationship is inconclusive.^{Endnote 281} A meta-analysis of 23 epidemiological studies presented a pooled odds ratio of 5.7 (95% CI: 4.1–8.0).^{Endnote 279} A more recent systematic review which included only studies with ≥100 cases reported a pooled relative risk of 2.5 (95% CI = 2.1–3.0), with consistent risks for B- and T-cell subtypes.^{Endnote 280}

The projected increases of the Atlantic region's rates in females were based on the long-term steeply rising trends starting with much lower levels in earlier periods and are therefore less likely to continue and result in rates higher than for all other regions. Incidence data from the early 1990s should be accurate.^{Endnote 282}

The causes of NHL are still largely unknown. Recent analyses describe the biological and clinical heterogeneity within the NHLs according to histology, suggesting that future epidemiological investigations need to focus on NHL risks and causal factors according to subtype.^{Endnote 283}