Canine uterine tumours: leiomyoma and leiomyosarcoma

For dogs, leiomyoma is the main uterine tumour to remember. It is a benign smooth-muscle tumour. Leiomyosarcoma is a malignant smooth-muscle tumour.

The short 90/10 recall cue needs its tumour group attached. Johnston and Tobias, second edition, gives leiomyomas as 90% of canine MESENCHYMAL uterine tumours. Leiomyosarcomas account for MOST of the remaining 10%. Mesenchymal describes the tissue-of-origin group. Those numbers do not make an exhaustive split of every uterine tumour; rare other types also occur.

Published summaries use different wording and denominators. The Veterinary Society of Surgical Oncology gives leiomyoma as 85–90% of canine uterine tumours. Keep these as approximate teaching proportions, rather than a fixed risk for an individual dog.

Cats have a different pattern. The textbook says feline uterine tumours are generally adenocarcinomas or arise from the endometrium, the uterine lining. The canine 90/10 cue should not be carried over to cats.

The outline of a uterine wall mass cannot establish whether a tumour is benign or malignant. Tissue histopathology is needed to establish the diagnosis.

References

Johnston and Tobias, Veterinary Surgery: Small Animal, second edition, chapter109; VSSO, Uterine Tumors Canine.