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Nasopharangeal carcinoma

Nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) arises from the epithelium of the nasopharynx, which is located deep within the head. The NPC exhibits distinct aetiology, epidemiology, and biology compared to other upper aerodigestive tract cancers. The deep location and diverse symptoms of NPC complicate early diagnosis, and its unique tumour biology necessitates different staging and treatment protocols. NPC is often described as an enigmatic tumour.

Epidemiology and Geographic Distribution

Nasopharyngeal cancer is a multifactorial disease influenced by genetic susceptibility, environmental factors, diet, and personal habits. It is most prevalent in southern China and Taiwan, with an incidence of 18% among American Chinese, compared to 0.25% in North American whites. Chinese individuals born in America have a lower incidence than those born in China. Contributing factors in China may include the burning of incense or wood, consumption of preserved salted fish, and a vitamin C-deficient diet, which protects against nitrosamine formation. In India, nasopharyngeal cancer is rare, accounting for only 0.41% (0.66% in males and 0.17% in females) of all cancers, with higher rates observed in the Northeast region, where the population is predominantly of Mongoloid origin. Individuals in Southern China, Taiwan, and Indonesia are at a greater risk for developing this cancer.

Aetiology of Nasopharyngeal Carcinoma (NPC)

The exact sequence of events leading to the development of nasopharyngeal carcinoma (NPC) remains unclear. The aetiology of nasopharyngeal carcinoma is multifactorial, and results from a complex interplay between genetic susceptibility, Epstein-Barr virus (EBV) infection, and environmental factors. Understanding these factors is crucial for developing effective prevention and treatment strategies for NPC.

  1. Genetic Factors. Genetic susceptibility plays a significant role in the incidence of NPC, particularly among individuals of Chinese descent. Even after migrating to regions with lower incidence rates, such as North America, they maintain a higher risk of developing NPC compared to the local population. This phenomenon suggests a strong genetic component, as evidenced by the familial clustering of cases observed in approximately 10% of NPC patients. While familial clustering may indicate genetic predisposition, it could also result from shared environmental exposures among family members.
  2. Viral Factors. EBV is closely associated with the development of NPC. Specific viral markers are being explored for screening in high-incidence areas. Two important EBV antigens are the viral capsid antigen (VCA) and early antigen (EA). IgA antibodies against EA are highly specific for NPC but have a sensitivity of only 70-80%, while IgA antibodies against VCA are more sensitive but less specific. Current research suggests that certain HLA subtypes may impair the immune response to EBV, allowing the virus to establish latent infections in the nasopharyngeal epithelium, which can lead to pre-malignant changes and eventually invasive cancer.
  3. Environmental Factors. Several environmental factors have been implicated in the aetiology of NPC. These include:
    • Air Pollution: Exposure to pollutants may increase cancer risk.
    • Tobacco and Opium Use: Smoking has been consistently linked to a higher incidence of NPC.
    • Dietary Factors: Consumption of preserved foods, particularly salted fish, has been shown to be carcinogenic due to high nitrosamine content. Laboratory studies indicate that feeding salted fish to rats can induce cancer, supporting its role in NPC development. Smoke from burning of incense and wood has been consistently linked to a higher incidence of NPC.

Pathology of Nasopharyngeal Cancer

Nasopharyngeal carcinoma (NPC) predominantly consists of squamous cell carcinoma (SCC), which accounts for approximately 85% of cases. Variants of SCC, such as transitional cell carcinoma and lymphoepithelioma, also fall under this category. Lymphomas represent about 10% of NPC cases, while the remaining 5% include rhabdomyosarcoma, malignant mixed salivary tumors, and malignant chordoma.

Histological Classification

The World Health Organization (WHO) has revised and classified nasopharyngeal epithelial malignancies into two types based on histological features observed under light microscopy.

  1. Type 1 – Well-differentiated keratinizing squamous cell carcinoma (25%) (WHO Type 1)
  2. Type 2 – Non-keratinizing carcinoma
    • Differentiated Non-keratinizing carcinoma (12%) (WHO Type 2)
    • Undifferentiated carcinoma Non-keratinizing (63%) (WHO Type 3)

Gross Presentation

NPC can present in three distinct forms:

  1. Proliferative: Characterized by a polypoid tumour that fills the nasopharynx, leading to obstructive nasal symptoms.
  2. Ulcerative: Characterized by a mass with abnormal capillaries on the surface with areas of ulceration. This form commonly presents with epistaxis (nosebleeds) as a prominent symptom.
  3. Infiltrative: Infiltrative growths extend submucosally, affecting surrounding tissues and no mass may be seen.

Spread of Nasopharyngeal Carcinoma

Local Spread. The most common site of origin for nasopharyngeal carcinoma (NPC) is the fossa of Rosenmuller. As the tumour is located in the central position of head, the tumour can spread locally in all directions:

  • Anterior Spread: It extends into the choana and nasal cavity, resulting in its blockage leading to nasal obstruction.
  • Inferior Spread: It extends into the oropharynx and hypopharynx.
  • Lateral Spread: It readily spreads to the parapharyngeal space and infratemporal fossa through the sinus of Morgagni.
  • Upward Spread: This involves extension towards intracranial structures via the foramen lacerum and foramen ovale, potentially affecting the middle cranial fossa and causing symptoms such as diplopia or ophthalmoplegia. The sixth cranial nerve is typically the first to be affected.
  • Sphenopalatine Foramen: Located anterior to the posterior choana, this foramen allows cancer from the lateral wall to spread to the pterygopalatine fossa.
  • Cavernous Sinus: From the pterygopalatine fossa, cancer can extend along the foramen rotundum into the cavernous sinus, potentially causing ophthalmoplegia.
  • Sphenoid Sinus: The thin floor of the sphenoid sinus makes it susceptible to invasion, allowing cancer to spread into the orbital apex and lead to eye symptoms.

Lymphatic Spread of Nasopharyngeal Carcinoma

The nasopharynx has a rich lymphatic network, which allows for early lymphatic spread of nasopharyngeal carcinoma (NPC) to cervical lymph nodes. This spread primarily affects ipsilateral nodes, although contralateral or bilateral nodes can also become involved.

The first echelon of lymphatic drainage from the nasopharynx is to the retropharyngeal lymph nodes, also known as the nodes of Rouvière. From these retropharyngeal nodes, lymphatic drainage continues in a step-wise manner to the upper jugular nodes and the upper posterior triangle nodes, ultimately progressing down to the lower neck. Lymphatic spread can occur either directly to these cervical nodes or indirectly through the involvement of retropharyngeal or parapharyngeal nodes. When the retropharyngeal nodes are affected, they can lead to additional symptoms, such as neck stiffness and torticollis.

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Reference Textbooks.
  • Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
  • Cummings, Otolaryngology-Head and Neck Surgery.
  • Stell and Maran’s, Textbook of Head and Neck Surgery and Oncology.
  • Ballenger’s, Otorhinolaryngology Head And Neck Surgery
  • Susan Standring, Gray’s Anatomy.
  • Frank H. Netter, Atlas of Human Anatomy.
  • B.D. Chaurasiya, Human Anatomy.
  • P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
  • Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
  • Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery.
  • Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
  • Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
  • Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.
  • Ganong’s Review of Medical Physiology.
Author:
Acoustic Neuroma

Dr. Rahul Bagla MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi) Fellow Rhinoplasty & Facial Plastic Surgery. Renowned Teaching Faculty Mail: msrahulbagla@gmail.com India

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