Clear cell odontogenic carcinoma

Clear cell odontogenic carcinoma (CCOC) is a rare malignant epithelial odontogenic neoplasm characterized by locally aggressive, infiltrative growth and a capacity for both regional and distant metastasis.[1][2] It arises centrally within the jaws, with a strong predilection for the mandible, and predominantly affects women in the fifth through seventh decades.[2][3] The tumor is composed of sheets and islands of glycogen-rich clear cells, and most cases harbor an EWSR1 gene rearrangement—most commonly an EWSR1-ATF1 fusion—which serves as a molecular hallmark and diagnostic adjunct.[4][5] Radiographically, CCOC typically presents as a poorly defined, expansile radiolucency with alveolar bone destruction.[2][3] Management centers on radical surgical resection; conservative treatment is associated with unacceptably high recurrence rates.[6][7]

• Current designation: Clear cell odontogenic carcinoma (CCOC), classified under malignant odontogenic tumors in the WHO Classification of Head and Neck Tumours (5th edition, 2022).[8][9]
• Historical names:
  • Clear cell odontogenic tumor — used in the 1992 WHO classification, which categorized the lesion as benign.[6]
  • Clear cell ameloblastoma — an older synonym occasionally encountered in the literature; now considered a misnomer because the entity is histologically and molecularly distinct from ameloblastoma.[2][10]
• The WHO reclassified CCOC as malignant in 2005 based on accumulating evidence of aggressive behavior, recurrence, and metastatic potential.[6][11]

• Frequency: Extremely rare; approximately 107 cases were documented in the world literature through 2018, and the tumor constituted 0.3% of odontogenic tumors in one large institutional series.[2][3]
• Age: Wide range; mean age at diagnosis approximately 54–57 years, with peak incidence in the fifth through seventh decades. Occasional cases occur in younger adults.[3][7][12]
• Sex: Female predominance, with reported male-to-female ratios ranging from 1:1.6 to 1:2.[3][7][13]
• Site:
  • Mandible far more common than maxilla (approximately 74–77% of cases).[2][7]
  • Within the mandible, both the posterior body and the anterior/premolar region are well-represented sites.[2][11]
  • Maxillary cases are less common and tend to involve the anterior region.[11][14]

Presentation and symptoms

• The most common presenting complaint is painless jaw swelling, reported in the majority of symptomatic patients.[2][3]
• Tooth mobility is a frequent associated finding, reflecting infiltrative destruction of the alveolar process.[1][3]
• Mild pain, gingival or periodontal changes, and decreased jaw opening are occasionally reported.[2]
• Sensory deficits (numbness, paresthesia) are uncommon, a feature that may help distinguish CCOC from metastatic renal cell carcinoma, in which sensory disturbance is more typical.[3]
• Rare presentations include a palpable neck mass as the initial sign.[2]

Tempo

Symptom duration before diagnosis is variable. Most patients seek care within 2 months to 1 year, though some cases have been present for several years before diagnosis.[2] The tumor generally behaves as a low-grade but relentless malignancy, with recurrences developing over months to many years.[15]

Complications

• Cortical perforation with soft-tissue extension is frequently observed at presentation.[6][14]
• Regional lymph node metastasis occurs in approximately 20% of reported cases; distant metastasis (most commonly pulmonary, occasionally hepatic or splenic) develops in a smaller subset, particularly after multiple recurrences.[1][15]

Location and distribution

• CCOC is a centrally located (intraosseous) jaw lesion with a strong predilection for the mandible.[2][3]
• Within the mandible, the posterior body is the single most common subsite, followed by the anterior/premolar region; some series report a roughly equal distribution between these zones.[2][11]
• Maxillary lesions are less frequent and tend to involve the anterior maxilla.[11][16]
• The lesion is typically solitary and unilateral.

Periphery and shape

• The hallmark radiographic appearance is a poorly defined, expansile radiolucency.[2][3][6]
  • Of 85 cases with available imaging data in the largest published summary, the vast majority (83 of 85) demonstrated a poorly defined expansive radiolucent pattern.[2]
• Margins are irregular and ill-defined, reflecting the infiltrative growth pattern.[11][14]
• The lesion may appear unilocular or multilocular (uni- or multicystic).[3]
• Occasional cases show variably well-defined margins, which can delay recognition of malignancy.[1]

Internal architecture

• The internal pattern is predominantly radiolucent without mineralized content.[2][6]
• Occasional cases exhibit a mixed radiolucent–radiopaque appearance, though this is uncommon.[6]
• No characteristic internal septation pattern has been established; when multilocular, coarse or irregular septa may be present.

Effects on teeth and adjacent structures

• Root resorption is a common finding and supports the diagnosis of a malignant or aggressive process.[3]
• Root divergence (displacement of adjacent teeth) is frequently observed.[3][12]
• Tooth mobility correlates with the radiographic finding of alveolar bone loss surrounding involved teeth.[1][2]
• Alveolar bone loss is a consistent feature, often mimicking advanced periodontal disease.[2][6]

Extent and cortical involvement

• Cortical expansion and perforation are characteristic; the tumor frequently breaches the buccal and/or lingual cortical plates.[6][11][14]
• Soft-tissue invasion beyond the cortex is common at presentation and may be underestimated on conventional radiographs.[6][14]
• CBCT or cross-sectional imaging can delineate the three-dimensional extent of cortical destruction and soft-tissue extension more precisely than periapical or panoramic radiographs, aiding surgical planning.[6]
• Perineural invasion, though a histologic finding, may manifest radiographically as widening of the inferior alveolar canal or mental foramen when present.[11]

Variants and atypical appearances

• Rarely, CCOC may present with relatively well-circumscribed margins, mimicking a benign odontogenic cyst or tumor.[1][17]
• Mixed radiolucent–radiopaque lesions have been reported but are exceptional.[6]
• Maxillary lesions may show extension into the maxillary sinus or nasal cavity on cross-sectional imaging.[14][16]

CT

• Contrast-enhanced CT demonstrates a hypodense to isodense expansile mass with irregular bone destruction and variable enhancement.[14][18]
• CT is superior to conventional radiography for evaluating cortical bone erosion, periosteal reaction, and the extent of soft-tissue invasion.[18]
• Assessment of cervical lymph nodes for regional metastasis is an essential component of CT staging.[18]

MRI

• MRI is preferred for evaluating bone marrow invasion, perineural tumor spread, and soft-tissue extent, particularly when the tumor approaches the skull base or involves the inferior alveolar nerve.[18]
• Signal characteristics are nonspecific; the solid tumor typically shows intermediate T1 and intermediate-to-high T2 signal with enhancement after gadolinium administration.

PET/CT

• FDG-PET/CT may be considered for staging when regional or distant metastasis is suspected, particularly in recurrent or advanced disease.[18]
• Pulmonary metastasis is the most common distant site and should be evaluated with chest CT.[1][13]

The differential diagnosis of an ill-defined intraosseous radiolucency of the jaws with clear cell histology is broad and includes both primary and metastatic neoplasms. Definitive distinction from other clear cell–rich tumors requires histopathologic examination supplemented by immunohistochemistry and, increasingly, molecular testing.[3][15]

The highest-risk diagnostic pitfall is failure to exclude metastatic renal cell carcinoma, which can present as the first manifestation of an occult renal primary. When a monophasic clear cell intraosseous jaw tumor is encountered, immunohistochemistry for PAX8, CD10, and vimentin (positive in RCC; negative in CCOC) and FISH for EWSR1 rearrangement should be performed before accepting a diagnosis of CCOC.[3][4][19]

Microscopic architecture

• CCOC is an unencapsulated, infiltrative neoplasm composed of islands, sheets, and cords of epithelial cells separated by thin fibrous septa that may show hyalinization.[1][3][11]
• The tumor invades medullary bone and frequently extends into surrounding muscle and perineural tissues.[3][11]

Histologic patterns

Three recognized patterns exist:[6][10]

• Biphasic (most common): Nests of large clear cells intermixed with smaller hyperchromatic polygonal cells with eosinophilic cytoplasm.
• Monophasic: Islands composed exclusively of clear cells.
• Ameloblastomatous (least common): Clear cell nests with peripheral nuclear palisading resembling ameloblastoma.

Cytologic features

• Clear cells are round to polyhedral with distinct cell borders, round nuclei, and optically clear cytoplasm resulting from intracytoplasmic glycogen accumulation (PAS-positive, diastase-sensitive).[1][3][11]
• Cellular pleomorphism and mitotic activity are generally low; when present, atypia tends to involve the eosinophilic cell component.[3]
• Necrosis is typically absent.[15]

Immunohistochemistry

• Positive: Pan-cytokeratin, CK19 (diffuse), CK14, p63, and epithelial membrane antigen.[7][11][12]
• Negative: Vimentin, S-100 protein, smooth muscle actin, desmin, HMB-45, CD10.[7][11]
• CK7 may show focal positivity.[12][14]
• Absence of intracellular mucin on Alcian blue–PAS staining helps exclude mucoepidermoid carcinoma.[14]

Molecular findings

• EWSR1 rearrangement is the molecular hallmark. FISH demonstrates EWSR1 rearrangement in the majority of tested cases (62.5–92% depending on the series), with EWSR1-ATF1 being the most common fusion partner.[4][23]
• EWSR1-CREM fusion has been identified as an alternative translocation in a smaller subset.[5]
• This translocation is shared with hyalinizing clear cell carcinoma of salivary glands and clear cell sarcoma, establishing a molecular link among these entities.[4][24]
• EWSR1 FISH or targeted RNA sequencing is a valuable diagnostic adjunct, particularly for the monophasic variant where morphologic overlap with other clear cell tumors is greatest.[4][5][6]

Radiologic-pathologic correlation

The poorly defined radiolucent margins on imaging correspond to the unencapsulated, infiltrative growth pattern with medullary bone invasion. Cortical perforation seen radiographically reflects direct tumor extension through cortical bone into soft tissues, a finding confirmed histologically in most resection specimens.[6][11]

Workup and referral

• Incisional biopsy is required for definitive diagnosis; fine-needle aspiration may be attempted but is diagnostically challenging.[6]
• Cross-sectional imaging (CT and/or MRI) of the primary site and neck is essential for surgical planning and nodal staging.[18]
• Chest CT should be obtained to evaluate for pulmonary metastasis.[1][13]
• EWSR1 FISH or molecular testing should be requested when the differential includes other clear cell neoplasms.[4][5]

Definitive treatment

• Radical surgical resection with clear margins (≥1 cm tumor-free osseous margin) is the standard of care.[6][7][15]
• Conservative treatment (curettage or enucleation) is associated with recurrence rates of approximately 71–87%, compared with approximately 29–48% after resection.[6][7][15]
• Neck dissection should be considered when there is clinical or radiographic evidence of cervical lymphadenopathy, perineural invasion, broad soft-tissue extension, or positive/close margins.[6][13]
• Adjuvant radiotherapy is a rational addition for cases with close or positive margins, soft-tissue invasion, or nodal metastasis, though evidence is limited to case series.[3][7][13]

Recurrence and metastasis

• Overall recurrence is reported in approximately 43% of cases (38 of 88 in the largest summary), with recurrence risk strongly influenced by the adequacy of initial surgery.[2]
• Recurrences may develop from months to over a decade after initial treatment (median approximately 6–8 years after resection).[15]
• Regional lymph node metastasis occurs in approximately 20% and distant metastasis (predominantly pulmonary) in approximately 17% of reported cases.[15]
• Multiple recurrences increase the risk of subsequent distant metastasis.[1][6]

Prognosis

• CCOC behaves as an unpredictable, at least low-grade malignancy with a protracted clinical course.[1][11]
• Tumor size, histologic pattern, presence of regional or distant metastasis, and local recurrence have been identified as significant prognostic factors.[25]
• Disease-specific mortality is approximately 10–21% in reported series, with death occurring up to two decades after initial diagnosis.[7][15]
• Long-term surveillance (clinical and radiographic) is mandatory given the potential for late recurrence.[2][7]

Molecular overlap with hyalinizing clear cell carcinoma

CCOC and hyalinizing clear cell carcinoma (HCCC) of salivary glands share the EWSR1-ATF1 fusion and monophasic clear cell morphology, raising the question of whether they represent the same entity arising in different tissue compartments.[4][22] Current classification maintains them as separate diagnoses distinguished primarily by site of origin: CCOC is intraosseous (odontogenic), whereas HCCC arises in minor salivary glands of the oral mucosa.[21][22] When a clear cell tumor with EWSR1 rearrangement involves both bone and soft tissue, careful clinicopathologic correlation is needed to determine the site of origin and guide appropriate classification.[15][22]