Spontaneous thrombosis of the left atrium is common in aged male and female Syrian (golden) hamsters in our laboratory and occurs at a younger age in females. At necropsy, the thrombus almost completely occludes the swollen atrium and is widely attached to the endocardium Endocrine manipulations unexpectedly influenced the occurrence of these thrombi. Following gonadectomy, development of such thrombi was hastened in male hamsters but was uninfluenced in female hamsters. Testosterone propionate given subcutaneously inhibited left atrial thrombosis in male and female gonadectomized hamsters. Norethynodrel with mestranol given subcutaneously to adult male hamsters was followed by an increased incidence of left atrial thrombosis. This increase may have been due to suppression of endogenous androgen production or action, or both. Microbiological studies of left atrial thrombi were negative. There was no correlation between the occurrence of left atrial thrombi and platelet numbers, prothrombin time, glass-tube clotting time, plastic-tube clotting time, or Russell viper-venom time. Partial thromboplastin time was lengthened in female but not in male hamsters with a left atrial thrombus.

Prolonged administration of norethynodrel with mestranol had a pronounced and selective influence on hormonal target tissues in middleaged male hamsters. Results were compatible with work in other species, which shows the primary site of action to be the pituitary-gonad axis. Markedly reduced gonadotrophin and androgen levels were indicated by atrophy of testes and accessory reproductive glands. The high dosage used also resulted in significant renal hypertrophy, but structural integrity was not conspicuously different from that of controls. The test agents had no influence on the incidence or metastatic propensity of a wide variety of spontaneous tumours, including adenomatous polyps and adenocarcinoma of the intestine, adrenal cortical nodular hyperplasia or adenoma, islet cell adenoma, melanoma, or adenocareinoma of Cowper's gland. This result is in accord with our previous observations that spontaneous tumorigenesis in the hamster is largely independent of hormonal physiology but is influenced by hormones to the extent that tumorigenesis may require some degree of normal tissue or cell integrity.

We have described the clinicopathologic findings in two cases of anorectal melanoma, and extracted the salient features from the medical literature. The disease is rare. Melanoma arises from the anal squamous membrane and very often spreads upward through submucosal planes, producing secondary satelites in the rectum. Trauma from defecation, vast lymphatic and venous systems in the anorectal region, and high invasiveness of the tumor cells eviden;ly account for early distant metastases. Histologically, the neoplastic cells often mimic other cancers. Treatment is surgical, with dismal end results.

Goitrogenesis and an increased frequency of cancer of the thyroid was induced by an iodine‐deficient rice diet or propylthiouracil. Goitrogenesis but not the occurrence of cancer of the thyroid was inhibited by supplementation of the rice diet with potassium iodide. Female hamsters were much more susceptible to goitrogenesis but not to cancer of the thyroid. Measures of thyroid function gave similar results in both sexes. Hamsters on the rice diet had normal serum PBI levels, markedly enhanced thyroidal affinity for 131I and subnormal or non‐detectable levels of serum inorganic‐iodide (I). Animals given propylthiouracil had subnormal levels of PBI, inconsistently subnormal thyroidal affinity for 131I and normal serum I. Serum calcium levels were subnormal in hamsters fed rice for 9 months or longer. The TSH‐dependent characteristics of thyroid tissue appear necessary for thyroid cancerogenesis but the relationship between marked hyperplasia, due to chronically high TSH levels, and the frequency of cancer of the thyroid is obscure for several reasons.