Cancer Incidence in Five Provinces of Iran: Ardebil, Gilan, Mazandaran, Golestan and Kerman, 1996-2000

Abstract

Syöpä on Iranin toiseksi yleisin ei-tapaturmainen kuolinsyy heti sydän- ja verisuoni-sairauksien jälkeen. Syöpätaakan arvioimiseksi syöpäilmaantuvuuden, -kuolleisuuden ja vallitsevuuden määrittäminen on ensiarvoisen tärkeää. Tämän tutkimuksen avulla pyritään kartoittamaan syövän esiintyvyyttä Iranissa sekä kehittämään ja testaamaan uutta menetelmää, jolla voidaan huomioida erot syöpärekisteröinnin kattavuudessa.

Retrospektiivinen tutkimus tehtiin viiden vuoden aikana 1996 - 2000 viidessä Iranin maakunnassa (Ardebil, Gilan, Mazandaran ja Golestan pohjoisessa sekä Kerman etelässä). Vuonna 1996 yhteensä 15.7 % Iranin väestöstä asui näissä maakunnissa. Saatavilla olevat syöpäpotilaiden sairaskertomus- ja kuolinsyytiedot koottiin syöpärekisteritietokannaksi. Tutkimuksessa kehitettiin myös ilmaantuvuuslukujen korjaamiseksi uusi menetelmä, joka perustuu muiden syöpien esiintyvyyslukujen vertaamiseen leukemiaan, jonka esiintyvyys on vakaa.

Tutkimusperiodin (5 vuotta) aikana todettiin 28,022 uutta syöpätapausta. Tavallisimmat miesten syövät olivat vatsalaukun, ruokatorven, virtsarakon, suoliston ja eturauhasen syövät. Naisilla yleisimpiä olivat rintasyöpä, vatsalaukun, ruokatorven, suoliston ja kohdunkaulan syövät sekä leukemia. Miesten kumulatiivinen vaara sairastua mihin tahansa syöpään 74 ikävuoteen mennessä oli 7.8 % ja naisten vastaavasti 6.4 %. Syövän esiintyvyys eri maakunnissa vaihteli. Ardebilissä vatsalaukun syöpä oli molemmilla sukupuolilla yleisin, Gilanissa miehillä virtsarakon syöpä ja naisilla suoliston syöpä, Mazandaranissa miehillä keuhkosyöpä ja naisilla rintasyöpä, Golestanissa ruokatorven syöpä molemmilla sukupuolilla ja Kermanissa ihosyöpä miehillä ja rintasyöpä naisilla. Syöpätapausten määrän arvioidaan kasvavan vuodesta 1996 vuoteen 2010 mennessä koko Iranissa 65 %. Naisten syöpätapausmäärän kasvu on jopa 95 % ja miesten 46 %. Kaikkiaan Iranissa todetaan vuonna 2010 noin 53 000 uutta syöpätapausta.

Tutkimuksen tietojen perusteella syöpäilmaantuvuus on Iranissa maailman alhaisimpia. 30 vuotta sitten tehdyssä kartoituksessa ruokatorven syövän vaara oli maailman korkeimpia. Nyt ruokatorven syövän ilmaantuvuus on pienentynyt kolmannekseen silloisista arvioista, mutta kaikkien muiden syöpien ilmaantuvuus on kasvanut huomattavasti.

Background

Cancer is the most common non-injury cause of death after cardiovascular diseases in Iran. Estimation of the burden of cancer in terms of incidence, mortality, and prevalence is the first step to plan control measures in every country but for almost 40 years there were no population-based cancer statistics in Iran to reveal cancer burden. This study is designed to ascertain the incidence of cancers in Iran, and develop and test a new method to adjust for ascertainment bias in the evaluation of cancer registry data.

Material and Methods

A retrospective survey in five provinces of Iran (Ardebil, Gilan, Mazandaran and Golestan in the north, and Kerman in the south) carried out for five years, 1996 2000. These provinces composed 15.7% of about 60 million population of Iran in 1996. Available medical records of cancer patients in public/private hospitals and diagnostic/treatment facilities, and death certificates of these five provinces were compiled, computerized and duplicate reports were eliminated. Eighty four percent of cases were microscopically verified and death certificate only (DCO) cases constituted 0.1% of cases.

Relative age-standardized ratio (RASR) was calculated by ASR of each cancer divided by ASR of leukemia. Adjusted relative age-standardized rate (ARASR with same unit as ASR) is calculated by multiplying the RASR for a specific cancer in a particular year by the sum of ASRs of that cancer over the years for which a trend is being determined and then dividing result by the sum of RASRs of the cancer for those years. Two likely assumptions are behind use of ARASR, first, constant ASR of leukemia over time, second, if under/over-registration occurs, it happens to all cancers in the same extent (random under/over-reporting).

Results

During the five years of study, there were 28,022 new cancer cases (57% men; 41.9% women; 1.2% unknown sex). The mean age at diagnosis was 55 (median age 60). In terms of age-standardized rate (ASR per 105), the most common cancers in men were stomach (22.5), esophagus (12.1), bladder (7.5), lung (6.5), colon/rectum (6.2) and prostate (5.6). The cumulative rate for 0 74 years of life in men was 7.8%. The leading female cancers were breast (13.3), stomach (9.3), esophagus (8.9), colon/rectum (6.0), leukemia (2.4) and cervical cancer (2.3). The cumulative rate for 0 74 years of life in women was 6.4%. In terms of incidence, Ardebil province had the highest rate for stomach cancer in both sexes, Gilan for bladder cancer in men and colorectal cancer in women, Mazandaran for lung cancer in men and breast cancer in women, Golestan for esophageal cancer in both sexes and Kerman for skin/hematological neoplasms in men and breast cancer in women. It is predicted that the annual number of new cases in year 2010 in Iran compared to 1996 will increase 65% (women 95%; men 46%) at least to 53,000 persons.

A new method was developed and tested on some complete and incomplete cancer registry data to adjust for ascertainment bias in cancer registry data. In registries with incomplete reporting, ARASR was a better estimate for time trend analysis. ARASRs in different countries or different times were comparable since they were already standardized for age structure. In addition, comparison between time trend of ASR and ARASR could be used to evaluate completeness of registration.

Conclusion

Generally the incidence of cancer in Iran was among lowest in the world. Cervical cancer was lower than even low risk countries such as China, Kuwait or Spain. Compared to 30 years ago, the incidence of esophageal cancer declined to approximately two thirds of its previous level in both sexes. However, the incidence of all other cancers increased dramatically up to 120%. Although this increase was unrealistically high, most likely because of under-registration of other malignancies than esophagus 30 years ago, the real change seems to be in the same direction but with slower slope.

The 65% predicted increase in the number of new cases by year 2010 is a huge burden for the health care system because by adding the number of old cases to these cases, the number of prevalent cancer patients will be substantially higher in 2010, especially in women.

The estimates by GLOBOCAN2002 and the results of this study were highly concordant because they shared the majority of their data sources except for Gilan (only available in this study) and Tehran (only in GLOBOCAN2002).

ARASR is more accurate than ASR in studying cancer incidence trends in registries with incomplete reporting. ARASRs in different countries or different times are comparable since they are age-standardized. Moreover, comparison between trend of ASRs and ARASRs can be used as a test for validity of registration.