Carcinoma ex Pleomorphic adenoma

CARCINOMA EX PLEOMORPHIC ADENOMA
  • 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
  1. Gary L.Ellis, Paul L Auclair. Tumors of the salivary glands. AFIP Atlas of Tumor Pathology. Series 4. 259-268
  2. Stacey E. Mills. Salivary glands. In: Sternbergs Diagnostic Surgical Pathology. 5th edition.
  3. Andersons