Addressing Etiological Factors of Nasopharyngeal Carcinoma in Kenyan Mountains

Introduction

The worldwide distribution of nasopharyngeal carcinoma (NPC) demonstrates substantial geographical and ethnic variation, with low incidence rates globally (1.5/100,000) and in most populations, but high rates in areas of southern China and southeast Asia (20/100,000),^{1 -3} north Africa (1-5/100,000), ⁴ and in Inuit populations of the Arctic (8.7-16.6/100,000). ⁵ The high incidence of NPC in these regions is associated with well-established elevated rates of etiological factors, including Epstein–Barr virus (EBV) infection, tobacco smoking, intake of salted fish and other salt-preserved foods, and occupational exposure to wood dust. ⁶ As with many other cancers, the incidence of NPC has been approximately estimated in numerous sub-Saharan regions (low-income countries), with incidence rates predominantly calculated from urban tertiary hospitals, thereby neglecting a representative portion of the semirural population. ⁷ The lack of accurate investigations in remote communities is becoming a health problem regarding recent data highlighting emerging cancer disease burden in such regions. ⁷ The remote communities of Kenyan mountains face to a high rate of NPC, despite the observation that populations in the region are not commonly exposed to typical etiological factors, including EBV infection, tobacco, salted foods, and wood dust. This observation was initially found in 1972 by Peter Clifford, who observed in 434 Kenyan patients from several remote communities that the highest NPC rates were found in tribes (Kipsigis, Nandi, Elgeyo, Kikuyu, Meru/Embu) living in the higher and consequently colder area of the country. ⁸ The author investigated potential etiological factors, reporting that tribal patients inhabited poorly ventilated, circular mud-and-wattle huts with grass-thatched roofs. Open wood fires for cooking and heating burned continuously throughout day and night. Without chimneys, smoke escaped inadequately through doors and roofs, creating high smoke concentrations that deposited soot across interior surfaces, resulting in chronic exposure to indoor air pollution. ⁸ At that time (1972), the author analyzed fire residues, revealing high concentrations of carcinogenic hydrocarbons, which were primarily attributed to the wood fuel used, derived from indigenous trees (acacias) and exotic afforestation species, mainly wattle and gums. These specific Kenyan wood fuel-related hydrocarbons were thought to possess particularly high carcinogenic potential, ⁸ while the Kenyan indigenous trees implicated in Clifford’s work are currently used in traditional medicine, for example, Prunus africana, Zanthoxylum gillettii, and Warburgia ugandensis. ⁹ Currently, most rural Kenyan households still use rudimentary indoor stoves for cooking (Figure 1), while many small-scale farmers continue burning plant and tree stumps implicated in the 1972 study. This under-investigated public health problem may support the increased NPC incidence in Kenya. The current estimated NPC incidence in Kenyan urban regions is 4.5/100,000, ranking 10th among national cancers.^10,11 Although this statistic remains approximate and probably underestimated as many rural regions (70% of the Kenyan population) are not included, this incidence is substantially higher than the worldwide rate.^10,11 Since Clifford’s study, the literature investigating etiological factors of NPC in remote sub-Saharan communities has not advanced, with no large epidemiological cohort studies confirming these preliminary observations. The population of sub-Saharan Africa and other African countries is growing, constituting an increased proportion of the world population, while Western country populations have decreased over the past decades. Addressing unresolved epidemiological questions for such common malignancies, which are additionally associated with worse prognosis, is important for future decades.

Figure 1.

Traditional indoor stoves for cooking. This photo was captured by Dr. Jerome R. Lechien during a Humanitarian Program conducted in Kenya (Iten Referral Hospital) from December 10, 2025 to January 01, 2026.