Sex difference in the incidence of nasopharyngeal carcinoma in Hong Kong 1983-2008: suggestion of a potential protective role of oestrogen.
BACKGROUND
Nasopharyngeal carcinoma (NPC) shows a male predominance in incidence while the underlying reasons have rarely been explored.


METHODS
We analysed incident cases of NPC recorded in Hong Kong Cancer Registry during the period 1983-2008. All cases were divided into 5-year age groups. Age group specific incidence rates of NPC by sex and male to female ratios in incidence rate by age group were calculated. A curve fitting approach was taken to quantitatively describe the age-specific incidence rates of NPC using non-linear regressions.


RESULTS
During the period 1983-2008, a total of 27,579 new cases of NPC were identified (20,060 males and 7519 females) in Hong Kong. The overall male to female ratio of the annual age-standardised incidence rates of NPC ranged 2.2-3.1. The male to female ratio of NPC incidence increased with age until peaking at ages 55-59 years and showed a decline thereafter. An additional minor increase at ages 15-19 years was also observed. Modelling of the age-specific incidence curves suggested divergent slopes for men and women and a delay in increasing incidence with age among females, by around 5-10 years before menopause ages.


CONCLUSIONS
The age-dependent pattern of the sex difference in the incidence of NPC could not be completely explained by known risk factors for NPC. The contributions of intrinsic exposures, such as sex hormones, merit consideration and further investigations.
School of Public Health and Primary Care, The Chinese of Hong Kong, Hong Kong SAR, China.
Shao-Hua
SH
Xie
Ignatius Tak-Sun
IT
Yu
Lap-Ah
LA
Tse
Oscar Wai-kong
OW
Mang
Li
L
Yue
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma; D002648:Child; D004967:Estrogens; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000453:epidemiology*; D012042:Registries; D012727:Sex Characteristics; D017678:Sex Distribution; D055815:Young Adult
D004967:Estrogens