Indian Journal of Cancer Medknow Publications on behalf of Indian Cancer Society ISSN: 0019-509X EISSN: 1998-4774 Vol. 48, Num. 4, 2011, pp. 406-409

Indian Journal of Cancer, Vol. 48, No. 4, October-December, 2011, pp. 406-409

Breast - Original Article

Age pattern of the occurrence of breast cancer in the northwest of Iran

J Eivazi-Ziaei¹, S Dastgiri², I Asvadi Kermani¹, A Nikanfar¹, A Esfahani¹, Z Sanaat¹, H Sadeghi-Bazargani³, J Vaez¹

¹ Department of Medicine, Hematology and Oncology Research Center, Tabriz, Iran
² Department of Medicine, Hematology and Oncology Research Center; Department of Community and Family Medicine, National Public Health Management Center, Tabriz, Iran
³ Department of Medicine, Hematology and Oncology Research Center; Department of Epidemiology and Biostatistics, Tabriz University of Medical Sciences, Tabriz, Iran
Correspondence Address: S Dastgiri, Department of Medicine, Hematology and Oncology Research Center; Department of Community and Family Medicine, National Public Health Management Center, Tabriz, Iran, saeed.dastgiri@gmail.com

Code Number: cn11117

PMID: 22293252
DOI: 10.4103/0019-509X.92256

Abstract

Breast cancer represents 27% of the cancers and 19% of the cancer deaths in female population. The aim of this study was to document the age pattern of the incidence of breast cancer in Iranian female population in the northwest region of the country. The study subjects were 1764 patients with breast cancer diagnosed/registered in the six university clinics between 1988 and 2008 in the northwest of Iran. The highest occurrence rates were observed for the birth year cohorts 1940-1949 (for 59-69 years old), 1950-1959 (for 49-58 years old), and 1960-1969 (for 39-48 years old). Among these three cohorts, the highest rate was observed in 1950-1959 birth year cohort (284.38 per 100,000 female populations, 95% CI: 260-310). This rate was significantly higher compared with the similar rates of other birth cohorts. There was no statistically significant difference between various years in terms of the average age at the diagnosis of breast cancer in our study setting. Despite the previous research reports, we found no significant difference between the mean ages at diagnosis of breast cancer from 1988 to 2008 in Iranian female population.

Keywords: Age pattern, breast cancer, incidence

Introduction

The highest occurrence of breast cancer occurs after age 35, with 83% of the cases occurring after age 50 with only 1.5% under age 30. ^[1] However, some Asian countries (i.e., Iran, India, Korea, southeast Asian region, and Arab world) are experiencing a different age pattern of disease (usually younger) at diagnosis compared with the patients in western developed countries. ^{[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15]} The proportions of young patients (i.e., 35 years or less) vary from about 10% in developed countries to 25% in some Asian countries indicating a poorer prognosis in the region. ^[10]

Yoo et al, ^[16] from Korea, reported an inverted V-shaped curve observed in some Asian countries, while the similar curve in western developed countries was almost linear increasing by age.

The aim of this study was to document the age pattern of the incidence of breast cancer in Iranian female population in the northwest region of the country.

Materials and Methods

This study was carried out in Tabriz Hematology-Oncology research center of the Tabriz University of Medical Sciences in the northwest of Iran. The study subjects were 1764 patients diagnosed/registered in the six university clinics between 1988 and 2008. In early years full data were not available because of the problems in registration system, while in latter years full data were recorded. Total female population of the area was obtained from the regional and national Bureau for Vital Statistics.

Descriptive statistics, survival model, and occurrence of breast cancer by birth year were calculated for the study population. Ninety-five percent confidence intervals (95% CI) were calculated to assess the statistical significance of the data.

Results

Occurrence of breast cancer (per 100,000 female populations) by birth year cohorts in three different age groups (2-40, 41-60, and 61+ years) was investigated in this study. The highest rates were observed for the birth year cohorts 1940-1949 (for 59-69 years old), 1950-1959 (for 49-58 years old), and 1960-1969 (for 39-48 years old). Among these three cohorts, the highest rate was observed in 1950-1959 birth year cohorts (284.38 per 100,000 female populations, 95% CI: 260-310). This rate was significantly higher compared with the similar rates of other birth cohorts. [Table - 1] shows the occurrence of breast cancer by birth years.

[Table - 2] and [Figure - 1] show the mean age at the diagnosis of breast cancer subjects. There was no statistically significant difference between various years in terms of the average age at the diagnosis of breast cancer in our study setting.

Discussion

In this study, the age pattern of the incidence of breast cancer in Iranian female population in the northwest region of country was investigated. No significant difference was found between the mean ages at diagnosis of breast cancer from 1988 to 2008. Occurrence of breast cancer by birth year cohorts in three different age groups was statistically significant.

The role of some risk factors for breast cancer has been investigated in the country in the recent years. Ebrahimi et al^[17] have shown that family history and marital status may have an impact on the incidence of breast cancer in Iranian women. A multivariate analysis in the northern Iran showed that higher education, late menopause, history of induced abortion, first-degree family history of the disease, and body mass index were all possible risk factors for the occurrence of breast cancer. Furthermore, having more episodes of full-term pregnancy, longer duration of breast feeding, and parity of two or more were shown to be protective factors for breast cancer. ^[18] Known risk factors of breast cancer may, however, vary slightly in different parts of the world. This may indicate that environmental factors might be of greater importance than genetic factors. ^[17]

In Iran, breast cancer affects women at least one decade younger than their counterparts in the western developed countries. ^[14] A multicenter research study on Iranian female population showed that the mean age of women with breast cancer was 48.8 years. The highest frequency of breast cancer was observed in the 40-49 age groups (31.8%), while 23% of the occurrence of disease was observed in women younger than 40 years. ^[14] Some other researches have reported similar findings in other parts of Iran and some Asian countries. ^{[2],[3],[4],[5],[6],[7],[8],[19]} Our study on a cohort of Iranian female population in the northwest region of the country, however, showed that the mean age of breast cancer has not considerably changed over the past two decades indicating that there might have not been considerable change in environmental factors over the same time period in the area.

Comparing the mean age at diagnosis for breast cancer can lead to a biased conclusion in different ways:

• Narrower time span of available information for cancer cases (1988-2008) compared with the wider time span for studying birth cohorts introduces two sources of bias in comparing mean age at diagnosis for different birth cohorts. The first is that those of earlier birth years have lower chance to be diagnosed at younger ages. If we consider a hypothesis that later cohorts are more likely to develop cancer at younger than 39 years of age, the probability of being caught by our registry will even be zero for one-third of the study population. The three first cohorts as 1920-1940 will have a zero probability and there will be an increasing probability trend for the later cohorts which will lead to a biased conclusion that cancer age is going to be decreased through the recent decades. Second, those of later birth years will have lower chance to be diagnosed at older ages and similarly the probability of being caught by our registry at later ages will be zero for a noticeable part of the study population. However, both of these biases are in the same direction; underestimating means diagnosis age for later birth cohorts.
• Those belonging to the later birth years may differ in medical care seeking behavior from the older ones due to some reasons such as ageism and lower literacy.
• Due to the slow progression behavior in breast cancer, even without considering the time span limitation in this study, the higher quality of diagnostic facilities in recent decades as well as improved public knowledge and implementation of screening programs in some countries may lead to reporting lower mean ages at diagnosis in recent decades just because of earlier detection of cases. It is, however, clear that although the screening programs in developing countries (including Iran) are not well planned and developed, the awareness of female population of breast cancer and its examination might have lead to an early age of diagnosis in the area.

In conclusion, we found no significant difference between the mean ages at diagnosis of breast cancer from 1988 to 2008 in our female cohort group indicating that breast cancer does not occur earlier in the study population. This is in contrast to what were previously reported from other studies in Iran and some other Asian countries. ^{[2],[3],[4],[5],[6],[7],[8],[15],[19]} Despite clinical follow-up of a relatively large birth cohort of breast cancer patients in this study, we cannot rule out the underlying role of underestimation in our findings. More studies are needed to investigate this.

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