Frequent Harderian gland adenocarcinomas in inbred white-footed mice (Peromyscus leucopus)

In 1997, three lines of inbred Peromyscus leucopus--GS109A, GS16A1, and GS16B--were acquired by the Peromyscus Genetic Stock Center. Since then, records have been kept on tumors detected by visible inspection of live animals. The inbred lines GS109A and GS16A1 presented tumors with frequencies substantially higher than that of the other inbred line or of random-bred P. leucopus stock. The average age of detection was 456 +/- 75 days (n = 24) for GS109A and 568 +/- 168 days (n = 12) for GS16A1 respectively. Surprisingly, the majority of the tumors (23 of 24 for GS109A and 8 of 12 for GS16A1) appeared to be Harderian gland lesions. During the same time period only a single tumor, a fibrosarcoma, was noted in the other inbred strain (GS16B), and one Harderian gland tumor was detected in the random bred stock. On the basis of the number of animals born to each group, tumor frequencies were approximately 22.7%, 8.3%, 0.67%, and 0.07%, for GS109A, GS16A1, GS16B, and randombred P. leucopus stock, respectively. The periocular tumors appeared to be highly malignant, with elevated mitotic indices, marked anaplasia, and metastases to regional lymph nodes and lungs. The tumors were readily transplantable to other animals of the same line. Among various other species, malignant Harderian gland tumors are relatively rare.