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

Chapter 4: Projections by Cancer Site

15. Testis cancer

Testis cancer was responsible for 1.0% of all new cancer cases in Canadian males, with an average of 825 new cases annually in 2003–2007 (Table 4.15.1). It was mainly diagnosed in young and middle-aged males, with just over 80% of cases found in those younger than 45.

Testis cancer was the most common cancer in males under 45, representing 14.1% of the male cancer cases in that age group during 2003–2007 (Figure 3.9, Figure 4.15.1). In this period, the incidence rate rose steeply from age 10 to 14, peaked at age 25 to 34, and then decreased quickly (Figure 4.15.1). The 5-year relative survival rate is high, at 97% in 2006–2008.^{Endnote 1}

The overall incidence rate of testis cancer in Canada increased steadily by 39%, from 4.0 per 100 000 in 1983–1987 to 5.6 in 2003–2007 (Figure 4.15.2).

However, the rate of increase has slowed slightly since 1993–1997. Between 1998 and 2007, the ASIRs for testis cancer increased significantly at 1.4% per year (Figure 3.1). The primary trends of the ASIRs in each region demonstrate increases. The ASIRs were higher in western Canada and lower in the east. The agespecific analysis indicates that ASIRs in Canada increased steadily for males under 55 and showed opposite trends for those above this age (Figure 4.15.3).

Overall incidence rates of testis cancer are projected to increase gradually until 2018–2022 and then level off (Figure 4.15.2). A similar pattern is predicted for Ontario and the Atlantic region but the turn point is 5 years later. Rates for the Prairies are expected to reach a peak 5 years sooner than the rest of the country, then decrease gradually, presenting the lowest incidence in the last 2 projected periods. In contrast, the rates in British Columbia and Quebec will rise persistently through the whole prediction period. British Columbia is predicted to experience the highest incidence rates from 2018–2022. Figure 4.15.3 illustrates that rates in all age groups under 75 are expected to increase, but at different levels. Rates in the youngest age group will approach a peak in 2018–2022 and then display a downward trend. The rates in men aged 75 or older are projected to stabilize or decrease slightly.

From 2003–2007 to 2028–2032, the ASIRs for testis cancer are expected to increase by 8%, from 5.6 to 6.0 per 100 000 (Table 4.15.2). The annual number of new cases is projected to rise by 30%, from 825 to 1070 (Table 4.15.1).

Comments

Similar to the trends we observed in Canada, large increases in incidence of testis cancer have been reported over the last 4 decades in many countries, including the US,^{Endnote 214} European countries,^{Endnote 215, Endnote 216} and Australia.^{Endnote 217} The increases are also predicted in Ireland,^{Endnote 2} England^{Endnote 218} and Nordic countries.^{Endnote 3, Endnote 35} No explanation for the increasing trends has been accepted.

The rate of testis cancer in males younger than 45 is increasing, but the longer-term trend shows a downturn. This result may be considered as a limitation of the Nordpred method in predicting rare cancers, especially for a site such as testis where rates are higher at relatively young ages. For testis cancer in Canada, the model indicates the coefficients for more recently born cohorts were positive so that assuming later birth cohorts have a zero value can result in a longer-term projection of lower rates.

The etiology of testis cancer remains unclear, possibly due to small sample sizes in the majority of studies. The major risk factor for testis cancer could hypothetically be due to an excessive exposure to certain hormones. Prenatal exposure to excess estrogens, adolescent exposure to high levels of male sex hormones and exposure to environmental hormone disruptors have been linked to elevated risk.^{Endnote 86} Syndromes noted for abnormal testis and urogenital development are known to increase risk. Germ cell tumours account for 95% of all testis neoplasms. Cryptorchidism causes about 5% to 10% of germ cell tumours cases and increases the relative risk by 2.5- to 15-fold.^{Endnote 52, Endnote 53, Endnote 219} A lower ratio of sex hormones (estrogens/ androgens) may be associated with a reduced risk of germ cell tumours.^{Endnote 220} Population-wide increasing exposure to estrogenic or other hormonally active (e.g. antiandrogenic) compounds may be in part responsible for the observed increase in testis cancer incidence.^{Endnote 221, Endnote 222}

About 2% of testis cancer cases may be explained by inherited genetic factors.^{Endnote 86} Males with a father diagnosed with testis cancer have a 3.8-fold increase in risk, and those with a brother diagnosed with the disease have a 7.6-fold increase in risk.^{Endnote 223}