Plasmacytoma Clinical: Solitary, dome-shaped, alopecic nodules, usually less than 2 cm. in diameter. Most common sites are the head and feet; may occur on gingiva. Average age of affected dogs is 10 years. Considered benign tumors, usually do not recur following surgical removal. Cytology: Round, eccentric nuclei with dense chromatin; bi- and trinucleate cells are common and characteristic. Abundant blue cytoplasm, often with prominent Golgi or perinuclear clear zone.