Page 648 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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Tumors of the Male Reproductive

System

JESSICA A. LAWRENCE AND COREY F. SABA

Canine Testicular Tumors has been made to apply this to canine tumors. 9,13,19–23 Sertoli

Prevalence/Incidence cell tumors and seminomas occur with higher frequency in
cryptorchid testes. 3,24,25
Testicular tumors are the most common tumors of the canine male Rarely, other cell lineages can give rise to testicular tumors
genitalia and account for approximately 90% of all cancers in the such as hemangiomas, granulosa cell tumors, teratomas, sar-
male reproductive tract. 1–4 In the intact male dog, the testis is the comas, embryonal carcinomas, gonadoblastomas, lymphomas,
second most common anatomic site for tumor development, with schwannoma, mesothelioma, and rete testis mucinous adenocar-
an overall prevalence ranging between 6% and 27%. 1,3–7 Many of cinomas. 26–30 Many dogs diagnosed with testicular cancer have
these reports are case series and involve dogs submitted for routine more than one primary tumor. 3,6,18,31 In three separate stud-
necropsy and/or castration for cryptorchidism, making compari- ies evaluating a relatively large numbers of dogs with testicular
sons between study prevalence data difficult. However, a recent tumors, between 4% and 20% of dogs had more than one type of
population-based study conducted in Norway, where elective cas- testicular tumor. 3,8,32
tration is rare, reported a similar prevalence of 7% for testicular
tumors. 8 Risk Factors
The rate of development of testicular cancer in humans has
increased in some populations over time and across successive Several factors may influence the development of testicular tumors
birth cohorts, and a similar phenomenon has been suggested in in the dog, including cryptorchidism, age, breed, and carcinogen
dogs. 7,9–13 One relatively recent population-based study published exposure. There is a significant association between cryptorchi-
in 2011 did not find increased rates of testicular tumors among dism and the development of Sertoli cell tumors and seminomas,
dogs; however, only an 8-year period was evaluated. Testicular but not interstitial cell tumors. 4,15,25,33 An early prospective epi-
8
tumors are most often diagnosed in geriatric male dogs with a demiologic study compared the incidence of testicular tumors in
median age of approximately 10 years. 1,3,4,14,15 cryptorchid dogs to age- and breed-matched control dogs. None
15
The three most common testicular tumors arise from dis- of the control dogs developed testicular tumors during the study,
tinct testicular subsets: sustentacular cells of Sertoli, the sper- in which the average duration of monitoring was 2 years. The inci-
matic germinal epithelium, and the interstitial cells of Leydig, dence of testicular neoplasia in the cryptorchid dogs was 12.7 per
giving rise to Sertoli cell tumors, seminomas, and interstitial 1000 dog-years at risk, whereas for cryptorchid dogs older than 6
cell tumors, respectively (Table 29.1). The World Health Orga- years the incidence increased to 68.1 per 1000 dog-years at risk.
2
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nization (WHO) classification of tumors of domestic animals Inguinal cryptorchidism may further increase the risk of testicular
differentiates the major types of testicular tumors in dogs as tumor development compared with abdominal cryptorchidism
sex-cord stromal tumors (Sertoli cell tumors, interstitial cell (Fig. 29.1). 4,15,25 In cryptorchid dogs, tumors more frequently
tumors), germ cell tumors (seminoma, teratoma), and mixed develop in the right testicle, potentially because the right testicle
germ cell–sex-cord stromal tumors. Sertoli cell tumors, inter- is more likely to be retained. 4,15,32 Chronologic age is a risk factor
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stitial cell tumors, and seminomas have historically developed for development of a primary testicular tumor; in one study, dogs
with equal frequency, although recent studies have suggested older than 10 years were more likely to develop tumors than dogs
that the prevalence of Sertoli cell tumors is lower, at 8% to younger than 6 years. Another study indicated that the detec-
15
16%. 1,3,4,7,17,18 Seminoma occurred most frequently in a study tion rate of testicular tumors in dogs younger than 10 years was
of lifetime occurrence of neoplasia in German shepherd dogs significantly associated with cryptorchidism, with more than 60%
and Belgian Malinois. Human testicular tumors are often of cryptorchid testicular tumors identified in middle-aged dogs
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divided into seminoma and nonseminoma, and seminomas are (6–10 years). 4
further differentiated as classical (SE), atypical, and spermato- Several breeds have been reported to have increased risk
cytic seminoma (SS) according to the WHO, and some effort of developing primary testicular tumors, including the boxer,

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