Squamous Metaplasia in Pleomorphic Adenoma: A Diagnostic and Prognostic Enigma

Abstract

Pleomorphic adenoma (PA) is the most common benign salivary gland tumor. Histologically, squamous metaplasia has been reported in PA, but has rarely been documented as being extensive enough to cause significant misdiagnosis. Here, we present an unusual case of PA in a 50-year-old female patient presenting with swelling on the postero-lateral aspect of the palate for a week. Histopathologically, the tumor exhibited the features of conventional PA with extensive squamous metaplasia and giant keratotic lamellae in cyst-like areas. Such exuberant squamous metaplasia and keratin can be a diagnostic and prognostic pitfall and lead to overtreatment of the patient.

Pleomorphic Adenoma in the Lower Lip: A Case Report and a Review

“…40 Sharma et al reported that fine needle aspiration of the tumor could be a cause of trauma and development of squamous metaplasia later. 39 In our case, there was no history of trauma, as the lesion was excised surgically with no prior traumatic investigations. The transformation of squamous metaplasia into squamous cell carcinoma cannot be excluded and should be considered in determining the prognosis.…”

“…This is an incidental finding in some benign and malignant tumors. 39 Its origin is not clear, and it has been associated with a traumatic event leading to infarction/ischemia and repair following infarction. 40 Sharma et al reported that fine needle aspiration of the tumor could be a cause of trauma and development of squamous metaplasia later.…”

Pleomorphic Adenoma with Extensive Squamous and Adipocytic Metaplasia Mimicking as Low Grade Mucoepidermoid Carcinoma on FNAC

“…Microscopically, mucous, sebaceous, oncocytic and squamous metaplasia, sometimes with the formation of keratin pearls, may be present, but the latter are rare. This extensive squamous metaplasia and keratin brought this tumor's diagnosis close to intracapsular (in situ) PA, muco-epidermoid carcinoma, adenoid or adeno-squamous cell carcinoma, conventional squamous cell carcinoma (SCC), carcinoma ex PA, and necrotizing sialometaplasia [2]. Pleomorphic adenomas, particularly of minor salivary glands of palate, may contain large areas of squamous and mucinous metaplasia, arising the suspicion of mucoepidermoid carcinoma.…”

“…Approximately 8% of PA involve the minor salivary glands, whereas palate is the most common site, accounting for 60-65% of cases. The incidence of pleomorphic adenoma in intraoral minor salivary glands is 40-50% [2,3].…”

“…It occurs over a wide age range, but the mean age is 43.6 years and the peak incidence is between fourth and fifth decades of life. Being pleomorphic, it exhibits the ability to differentiate into epithelial (ductal and nonductal) cells and mesenchyme-like tissue (chondroid, myxoid and osseous) [2]. Thus, it is composed of a mixture of glandular epithelium and myoepithelial cells within a mesenchyme-like tissue, and the proportion of each component varies widely among individual tumors [1].…”