It is a carcinoma that shows the histologic evidence of tumor arising in benign pleomorphic adenoma
Incidence is of 3.6% of all salivary gland tumors, 11.6% of all malignant tumors and 2.8 to 42.4% of malignant salivary gland tumor
It is the 6th most common salivary gland malignancy
Malignant transformation occurs in 2% to 7% mixed tumor
In this tumor only the epithelial component is malignant unlike carcinosarcoma where both epithelial and mesenchymal component are malignant
Frequency of occurence of this tumor in the order of frequency is
Parotid – 67%
Submandibular gland – 15%
Sublingual – less than 1%
Minor salivary glands – 18%
Malignant transformation occurs in tumors having longer duration, with recurrence, advanced age and larger tumor size.
Age- Carcinoma ex pleomorphic adenoma occurs a decade later than that of benign mixed tumor. More common in 6th and 7th decades (but can occur in any age)
Sex – shows slight female predominance.
Clinical features
Presents as painless mass
Slowly growing mass with sudden increase in size and pain should rise the suspicion of malignancy
Patients may present with pain or fascial nerve palsy
20% of patients give the history of previous surgery
Gross findings
Proportion of benign and malignant components influences the gross appearance
Carcinoma ex pleomorphic adenoma is poorly circumscribed tumor or encapsulated with focal capsular infiltration
Size ranges from 1 to 25cms
carcinomatous components show gray white areas with areas of hemorrhages and necrosis where as the benign component appears as translucent gray blue areas
Microscopic findings
Benign component of the tumor shows myxoid and hyalinized stroma with proliferating epithelial cells arranged in tubules or cords
Carcinomatous elements show pleomorphism and infiltration into surrounding tissue.
Different growth patterns include glandular, solid, spindle cell or squamous type
Carcinomatous element is composed of cells having hyperchromatic nuclei with nucleoli and show high mitotic rate
Tumor cells show perineural and vascular invasion
Prominent hyalinization is common.
High grade tumors show necrosis
Most common carcinoma component in carcinoma ex pleomorphic adenoma is high grade adenocarcinoma or undifferentiated carcinoma
Other components are ductal carcinoma, polymorphous low grade carcinoma (Terminal duct), myoepithelial carcinoma and unclassified carcinoma
Other rare types include mucoepidermoid, epidermoid carcinoma, adenoid cystic carcinoma, adenosquamous carcinoma, epithelial- myoepithelial carcinoma, clear cell adenocarcinoma, acinic cell carcinoma and sarcomatoid carcinoma
In the early stages when the tumor is confined with in the capsule then it is termed as Non-invasive or preinvasive or encapsulated or in-situ carcinoma ex pleomorphic adenoma .
Features suggesting malignant transformation in benign tumor are
Overtly invasive growth
Vascular or perineural invasion
Necrosis
Prominent cytologic atypia with atypical mitotic figures
Large areas of hyalinization in benign mixed tumor indicates malignant transformation and extensive sectioning should be given to identify the malignant component
Earliest microscopic evidence of malignant transformation is often characterized by tumor cell aggregates embedded in the hyalinized stroma
Multiple tumor nodules, local recurrence, increased cellularity, apparent lack of encapsulation and small foci of capsular invasion does not indicate malignancy
Treatment and prognosis
It is extremely aggressive tumor
Recurrence occurs in 40% to 50% of patients
Proportion of tumor involved by carcinoma affects prognosis
Distance of invasion from capsule is important prognostic factor. Invasion of more than 8mm past the benign component is associated with bad prognosis
If the tumor extends beyond 6mm, local recurrence occurs in 70% of cases
Tumor confined with in the capsule has better prognosis than the tumor penetrating capsule which has poor prognosis
Grades and type of malignancy also affects the prognosis. Ductal carcinoma has better prognosis than the undifferentiated carcinoma which has poor prognosis
25% of patients develop metastasis to cervical lymph node. distant metastasis occurs to the lungs, bone (especially spine), abdominal area and central nervous system
Treatment is surgical resection with contiguous lymphnode dissection and adjuvant radiation therapy
References
Gary L.Ellis, Paul L Auclair. Tumors of the salivary glands. AFIP Atlas of Tumor Pathology. Series 4. 259-268