Screening Test for Nasopharyngeal Cancer (NPC): What Do We Know?

By: Dr Sandeep Rajan, Senior Consultant, Dept of Medical Oncology, NCC

Like most cancers, the cause of nasopharyngeal cancer (NPC) is multifactorial. Possible environmental or cultural factors that may be associated with NPC include the ingestion of Cantonese-style salted fish and preserved foods containing cancer-causing chemicals like nitrosamines, especially during childhood. Evidence of a virus called EBV in a majority of NPC cells has suggested a close association of this virus with this cancer.

Usually this type of cancer is detected only very late in its progress because of its obscure location in the body and the lack of signs and symptoms. Early symptoms could be minimal or non-specific like blocked nose, nosebleed etc. Hence, more than two thirds of patients are diagnosed late when neck lumps have developed or cancer has spread into deeper structures or distant organs. Though radiotherapy alone or combination with chemotherapy may still induce remission, however relapse rates are high and are associated with increasing resistance to therapy. Earlier detection would almost certainly improve overall survival, as in early stage survival may be 70-90%.

Since EBV has a direct role in the type of NPC prevalent in Singapore, this relationship to detect the tumour by tracing the virus is feasible. Numerous studies done in Singapore, Hong Kong, Taiwan and Canada have shown that certain antibodies developed in response to the virus or detecting the genetic signature of EBV virus in blood, nose or throat scrapings are more prevalent in patients with NPC as compared to normal people. Some of these tests may have 90-99% accuracy in predicting the risk of this cancer when positive but in 5-15% this test may be negative yet cancer may be present.

However, when these tests are applied to people at high risk of developing NPC, like those with symptoms or many inflicted family members, major pitfalls are that these tests could be positive in some other cancerous conditions too and in some cases, the test may be positive for many years before cancer is detected. This not only makes such testing very expensive, but it can also kindle a lot of unnecessary anxiety.

Furthermore, NPC can inflict the very young as well; hence the minimum age to start such screening is not known. Therefore, until large population based screening tests have proven efficacy of screening tests for NPC, it is recommended that these tests be offered only as a research study and after careful counselling.