Dear Editor,

I have read the comments with great pleasure that were made by Irfan Mohamad and Sanjeevan Nadarajah with regard to our paper, Nasopharyngeal Carcinoma in Oman: A Descriptive Analysis, which was published in the May issue of the Oman Medical Journal.1

The total number of patients included was 26 over an eight year period, which included all new and old cases.

Your letter compared data from Oman and Malaysia and it is important to consider the population difference between these two countries. The total population of Omanis in Oman is 2.3 million according to the 2014 population census.2 However, the population of Malaysia is almost 30 million.

Unlike your study, we had no cases of nasopharyngeal carcinoma (NPC) in the pediatric age group. NPC has been noted to exhibit a bimodal distribution with an early peak in age-incidence curves observed in certain geographically disparate populations. This suggests that there are distinct causal entities and the possible exhaustion of susceptible individuals from the population at a certain age.3 In most cases, the first peak is noted in late adolescence/early adulthood (ages 15–24 years) followed by a second peak later in life (ages 65–79 years), which corresponds to your observation.

Neck mass is the most common presentation worldwide for which the findings were similar.4 No cases were reported presenting with cranial nerve involvement in Oman though most presented at an advanced stage of the disease. The incidence of cranial nerve involvement in NPC varies according to the region but the worldwide incidence is around 10%.5 None of our cases (total of 10) presented with cranial nerve involvement but three cases presented with distant metastasis.

The incidence of NPC worldwide ranges from 1–25:100,000, which tends to be higher in South Asia and parts of China.6

Disclosure

No conflicts of interest, financial or otherwise, were declared by the author.

references

1. Al-Azri A, Al-Sheibani S. Nasopharyngeal Carcinoma in Oman: A Descriptive Analysis. Oman Med J 2015 May;30(3):167-172.
2. Parkin DM, Whelan SL, Ferlay J, Teppo L, Thomas D. Cancer incidence in five continents. Volume VIII. IARC Scientific Publication No. 155. IARC Press; 2003.
3. Bray F, Haugen M, Moger TA, Tretli S, Aalen OO, Grotmol T. Age-incidence curves of nasopharyn-geal carcinoma worldwide: bimodality in low-risk populations and aetiologic implications. Cancer Epidemiol Biomarkers Prev 2008 Sep;17(9):2356-2365.
4. Imad K, Iqbal M. Muhammad AY. Presentation of Nasopharyngeal Carcinoma. Available at: www.jpmi.org. pk/index.php/jpmi/aticle/view/24. Accessed January 2011.
5. Lo SS, Lu JJ. Natural History, Presenting Symptoms and Diagnosis of Nasopharyngeal Carcinoma. In: Lu JJ, Cooper JS, Le AWM. Nasopharyngeal Cancer Multidisciplinary Management. Medical Radi-ology 2010. p. 44-45.
6. Chang E, Adami H. Nasopharyngeal Carcinoma. In: Adami H, Hunter D, Trichopoulos D. Textbook of Cancer Epidemiology. 2nd Edition. Oxford University Press; 2008. p. 177-179.