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A 68-year-old man with a recurrent orbital lesion
Digital Journal of Ophthalmology 2009
Volume 15, Number 4
September 2, 2009
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Marc-Andre Rheaume, MD | University of Montreal
Guy Allaire, MD, FRCPC | University of Montreal
Akram Rahal, MD, FRCSC | University of Montreal
Vijayabalan Balasingam, MD, FRCSC, PhD | University of Montreal
Patrick R. Boulos, MD, FRCSC | University of Montreal
Diagnosis and Discussion
Carcinoma ex-pleomorphic adenoma (malignant mixed tumor)

Lacrimal gland lesions constitute almost 10% of all space-occupying orbital lesions. Between 50 and 80 percent are inflammatory or lymphoid tumors. Epithelial tumors, of which approximately 55 percent are benign and 45 percent malignant, represent the vast majority of remaining lesions.(1,2)

Pleomorphic adenoma is the most common benign neoplasm of the lacrimal gland, and it is almost always found in the orbital lobe of the gland. It tends to affect men slightly more than women. Typically, a patient between 40 and 50 years of age will present with a slowly progressive and painless proptosis. Globe dystopia is commonly seen. Orbital imaging shows a well-circumscribed mass usually without bony erosion. Histopathologically, these lesions consist of a mixture of epithelial, myoepithelial and mesenchymal elements that led to the term benign mixed tumor. Management consists of complete surgical excision of the tumor with its pseudocapsule and a surrounding margin of orbital tissue. Incisional biopsy prior to surgery should be avoided. One series found a recurrence rate of 32 percent at 5 years in previously biopsied lesions, compared to 3 percent for those without biopsy.(3) This surgical dictum has however come under recent debate.(4)

Of recurrent pleomorphic adenomas, it is estimated that 10 percent will become malignant after 20 years and that 20 percent will become malignant after 30 years.(3) Malignant transformation will result in a malignant mixed tumor, termed carcinoma ex-pleomorphic adenoma. Patients are typically older than those with pleomorphic adenoma, and they present with a rapidly growing painful lesion. Bony erosion is commonly seen on orbital imaging. Histopathologic diagnosis can only be made if one has either earlier biopsy evidence of a pre-existent pleomorphic adenoma, or if the coexistence of vestiges of a pleomorphic adenoma is seen along with the outgrowth of a malignant clone in the material.(5) Most commonly, the malignant epithelial elements will be a poorly differentiated adenocarcinoma, but adenoid cystic carcinomas have also been described.(6) Incisional biopsy is recommended to confirm the diagnosis and a systemic workup for metastasis should be conducted. Malignant mixed tumors that have invaded beyond their capsule carry a poor prognosis, with a survival rate at 5 years of only 35 to 45 percent.(7) Management consists of some form of radical exenteration followed by adjunctive radiotherapy. As regional metastases have been described months after orbital surgery, it might be advisable to perform parotid and cervical lymph node dissections at the time of the first intervention.(5)

This case illustrates the potentially devastating hazards of an incompletely resected pleomorphic adenoma. It is important that such tumors be completely excised during the initial surgery to prevent recurrences and possible malignant transformation.
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