Which of the following is not true about the pleomorphic adenoma of parotid gland?

Superficial parotidectomy is the treatment of choice The ratio of malignant to benign tumors by the as well: parotid gland, 80% benign and 20 % malignant; Submandibular gland and sublingual gland, 50% benign and 50% malignant; and minor salivary glands, 25% benign and 75% malignant Facial nerve palsy is an infrequent presenting complaint and indicate malignancy. Pleomorphic adenoma (mixed tumor): This is the commonest tumor of the major salivary gland and its marked feature id histological diversity. It is called mixed because beside epithelial element there is also myxoid, hyline, chondroid (cailaginous) and even osseous bone. About 90% of pleomorphic adenoma is seen in parotid gland ,7% is seen in submandibular gland. tail of the parotid is commonest location in the tail of parotid. Nature of tumor: It is basically a benign tumor. Recurrence rate, which is repoed to be high, was mostly due to fault in the surgical technique in the form of simple enucleation which was often used earlier. The incidence of malignant transformation increases with the duration of the tumor, being 2% for tumors present with less than 5 years duration and 10% for those of more than 15 years duration. Treatment: This tumor is radioresistant, so excision is treatment of choice. Superficial parotidectomy is the treatment of choice, this operation is known as patey's operation. In case of submandibular gland neoplasm, the whole gland is excised with paicular care to preserve the lingual and hypoglossal nerve. Ref: L & B 25/e, page 761-62 ; Sabiston 18/e, page 834-36 ; Robins 7/e, page 791-92 ; Textbook of surgery by S. Das 5/e, page 607-609