Abstract
INTRODUCTION AND IMPORTANCE: Nasopharyngeal carcinoma (NPC) is considered a rare malignant head and neck tumour. However, the importance of genetics and environmental factors in the epidemiology of NPC is still unclear. Twins represent an excellent study population for genetic epidemiology; this is especially true of monozygotic-type twins because they are genetically identical. The difference in cancer occurrence between monozygotic twins is typically interpreted as a result of possible environmental factors. CASE PRESENTATION AND CLINICAL DISCUSSION: We present the first case report of monozygotic twins with NPC. The twins' significant features are homogenous presentation, tumour location (both left-sided) and identical histology; therefore, the prognoses may be similar. Environmental factors could not be addressed in these twins because they shared the same background, and at the same time, they had no potential known contributing factors. CONCLUSION: Having one of the twins affected is a strong and easily recognisable risk factor for developing NPC in the other. This strong association suggests the need for regular screening of the second twin for early diagnosis of NPC.