Malignant Tumors of the Base of Tongue Workup

Updated: Apr 05, 2021
  • Author: Rishi Sethia, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
  • Print

Laboratory Studies

HPV testing with p16 immunohistochemistry is now required for all newly diagnosed base of tongue SCCs, with p16 overexpression being strongly associated with high-risk HPV. Additional HPV testing via in situ hybridization or polymerase chain reaction (PCR) assay can be utilized to clarify HPV status, if warranted. [18, 19]


Imaging Studies

CT scanning and MRI

Cross-sectional imaging is an important tool for the diagnosis and clinical staging of malignant tumors of the tongue base. High-resolution computed tomography (CT) scanning of the neck with intravenous (IV) contrast is the most commonly utilized modality and has the advantages of increased availability and speed, with excellent spatial resolution, demonstration of bone infiltration, and lymph node visualization. CT scanning of the chest is often obtained in addition to neck CT imaging as standard protocol for staging purposes, to assess for pulmonary metastases.

Magnetic resonance imaging (MRI) of the neck is more costly but can be utilized as an alternative to neck CT scanning. In certain instances, it is the preferred modality for deeply invasive malignancies, offering superior soft tissue evaluation and multiplanar capabilities. [20]  

PET/CT scanning

Positron emission tomography (PET) scanning with CT imaging is used in the evaluation of unknown primary tumors, synchronous primary tumors, and distant metastases. [5]  For surveillance following treatment of oropharyngeal cancer, PET/CT scanning is the most sensitive and specific imaging modality and plays an important prognostic role, especially when obtained between 3-6 months and 12 months posttreatment. [21]  (See the image below.)

An axial positron emission tomography (PET) scan s An axial positron emission tomography (PET) scan shows asymmetrical hypermetabolic uptake within the left base of the tongue/tonsillar region consistent with a primary tumor. Intense hypermetabolic left cervical lymphadenopathy is also seen and is concerning for metastatic disease.


Ultrasonography (US) offers distinct advantages as an inexpensive, radiation-free, real-time modality that can be used for evaluation of cervical lymphadenopathy and is potentially useful for guidance of fine-needle aspiration (FNA). However, the previously mentioned imaging modalities are favored for a comprehensive assessment.


Diagnostic Procedures

Biopsy via endoscopic examination of the primary site with the patient under anesthesia remains the definitive procedure to establish the diagnosis and accurately assess the primary tumor. Panendoscopy including direct laryngoscopy and esophagoscopy is often performed to assess for the extent of the lesion and to rule out secondary primaries, in order to help determine therapeutic management options. If lymphadenopathy is discovered on examination or imaging, FNA can provide a minimally invasive and expedited diagnosis as well.


Histologic Findings

The most common malignant neoplasm of the base of the tongue is SCC. The World Health Organization (WHO) classifies oropharyngeal SCC as HPV-positive or HPV-negative. HPV-associated oropharyngeal SCC frequently lacks keratinization and mature squamous differentiation, unlike the traditional, keratinizing SCC associated with tobacco and alcohol use. [22]

Other, less common malignancies include salivary gland tumors such as mucoepidermoid carcinoma, adenoid cystic carcinoma, and polymorphous adenocarcinoma, and hematolymphoid tumors, which include various forms of lymphoma. [23]  Rarely, lymphoepithelial carcinoma, soft tissue tumors, small cell neuroendocrine carcinoma, adenocarcinoma, or metastatic lesions can be found in the base of tongue. [1, 22]

Extranodal non-Hodgkin lymphoma of the head and neck is a relatively uncommon disease. If the nasopharynx (16% of the lymphomas), tonsils (12%), and base of tongue (8%) are grouped together, this combined site (Waldeyer's ring) becomes the most common location of the disorder (36%). [24]  Most Waldeyer's ring lymphomas express the B-cell phenotype. The clinical features and immunohistologic findings suggest that Waldeyer's ring lymphomas, other than those of the nasopharynx, share some of the characteristics of mucosa-associated lymphoid tissue lymphomas.

In difficult cases, detection of monoclonal immunoglobulin, an absence of keratin staining, and a lack of epithelial features based on electron microscopy findings are useful adjuncts for diagnosis. Three fourths of the patients have stage I or II disease, and approximately two thirds of them have intermediate-grade lymphoma. Patients with lymphomas of high histopathologic grade and recurrent and disseminated disease have the poorest prognosis. [24]



The American Joint Committee on Cancer (AJCC) utilizes the tumor, node, metastasis (TNM) system to stage oropharyngeal carcinoma based on the size of the primary site tumor, involvement of adjacent structures, involvement of regional lymph nodes (LNs), and presence of distant metastasis. Moreover, HPV (p16) status was incorporated into the eighth edition of the AJCC Cancer Staging Manual. The staging system for oropharyngeal carcinoma, as contained in the manual's eighth edition, is outlined below. [25]

All measurements listed below are in greatest dimension.

Primary tumor (T)

See the list below:

  • T1 - ≤2 cm
  • T2 - >2 cm but ≤4 cm
  • T3 - >4 cm or extension to lingual surface of epiglottis

Non–HPV-associated (p16-negative)

  • T4a - Moderately advanced local disease; invades adjacent structures (larynx, tongue muscles, medial pterygoid muscle, hard palate, mandible) or beyond
  • T4b - Very advanced local disease; invades lateral pterygoid muscle, pterygoid plates, lateral nasopharynx, skull base, or carotid artery encasement

HPV-associated (p16-positive)

  • T4 - Moderately advanced local disease; invades adjacent structures (larynx, tongue muscles, medial pterygoid, hard palate, mandible) or beyond

Regional lymph nodes (N)

See the list below:

  • Nx - Regional lymph nodes cannot be assessed
  • N0 - No regional lymph node (LN) metastasis

Non–HPV-associated (p16-negative)

  • N1 - Metastasis in single ipsilateral LN ≤3 cm and extracapsular extension (ECE)–negative
  • N2a - Metastasis in single ipsilateral LN >3 cm but ≤6 cm and ECE-negative
  • N2b - Metastasis in multiple ipsilateral LNs, none >6 cm, and ECE-negative
  • N2c - Metastasis in bilateral or contralateral LNs, none >6 cm, and ECE-negative
  • N3a - Metastasis in LN >6 cm and ECE-negative
  • N3b - Metastasis in any LNs and clinically overt ECE-positive

HPV-associated (p16-positive)

Clinical staging

  • N1 - 1+ ipsilateral LNs, ≤6 cm
  • N2 - Contralateral or bilateral LNs, ≤6 cm
  • N3 - Any LN(s) >6cm

Pathologic staging

  • N1 - Metastasis in ≤4 LNs
  • N2 - Metastasis in >4 LNs

Distant metastasis (M)

See the list below:

  • Mx - Distant metastasis cannot be assessed
  • M0 - No distant metastasis
  • M1 - Distant metastasis