Rocky looks to be a Maine Coon cat: he adopted a suburban family as a half-grown stray kitten 2 years ago, and has lived in their garage ever since as an "inside/outside" cat. He presents at the emergency clinic with a history of anorexia lasting three days, and severe dyspnea of 12 hours' duration: the owner found him lying on the floor of the garage, laboring to breathe, picked him up and rushed him in.

Radiographic examination reveals significant pleural effusion, and increased opacity in the cranial thoracic cavity. A complete blood count (CBC) revealed nothing unusual. Test for Feline Leukemia Virus (FeLV) was positive. Thoracocentesis for cytological examination and clinical relief showed an effusion consisting of cells with large numbers of mitotic figures, and scanty highly-basophilic cytoplasm. A diagnosis of mediastinal lymphoma secondary to FeLV infection was made and Rocky was moved to the ICU for supportive care, and after two days released to his owner again when the symptoms were alleviated. Six days after discharge he was brought back to the clinic and euthanized at the owner's request. A necropsy was performed.

Points to ponder:

1. What cell types are involved in the development of this cat's condition, and what's the likeliest series of events that has happened?

2. How can you determine the cellular origins of the tumor?

3. The fact that Rocky is FeLV positive is significant. Why?

4. The owner should be given advice and guidance: what should that advice be?