Good news - benign. Here is what the vet said as she can't help it. :-)
Hi, Please see the results of the biopsy on Risa's ear mass. Locally invasive benign tumor. Unfortuntely, because Lex tried to salvage the end of the ear, there is incomplete excision. If it grows back, ear amputation would be required. We will see how it goes. We hope she has recovered well.
From what I read from Idexx it is a sebaceous cyst. Why the ear would have to be amputated, I am not sure. She tends to lean towards the worst case scenario. Lex does not.
MICROSCOPIC DESCRIPTION: Sections of this mass are characterized by a proliferative population of basaloid epithelial cells forming discrete nodular masses supported by a robust fibrovascular stroma. Moderate numbers of lymphocytes and plasma cells are noted within the supporting stroma. These basaloid epithelial cells frequently differentiate to produce nodules of sebaceous cells and ductular structures. There is no significant cellular atypia and infrequent mitotic activity (4 per 10 400 X). These proliferative cells extended to the hemorrhagic margins of the examined section.
MICROSCOPIC INTERPRETATION: Sebaceous gland epithelioma; excision incomplete
COMMENT: Sebaceous gland epitheliomas are relatively common neoplasms of dogs that arise from the basaloid reserve cells of sebaceous glands. These tumors are usually solitary firm nodules or plaque like masses that are often ulcerated. They most often occur in the skin of the head, eyelids, dorsal neck, and back. As with sebaceous adenomas, Cocker Spaniels and Poodles have a higher incidence of these lesions. Sebaceous epitheliomas have similar biologic behavior to basal cell carcinomas and are considered to be a low grade malignancy; thus, they are locally aggressive but rare to metastasize.