Malignant seminoma with gross metastases in a dog

A 10-year-old male crossbred dog developed a non-painful unilateral testicular swelling; the other gonad was reduced in size. Both gonads were removed surgically; the larger contained a diffuse seminoma, the smaller atrophic testis contained an interstitial cell adenoma and several intratubular seminomas. Six months after being castrated the dog developed palpable intraabdominal masses. Necropsy revealed gross metastatic malignant seminoma in para-aortic lymph nodes. No histological features were identified to correlate with the malignant behaviour of this usually benign tumour.