Disputas Cand.Med Sanda Krum-Hansen

Avhandlingen er tilgjengelig her! The doctoral thesis! Prøveforelesning over oppgitt emne holdes kl. 09.15:  «“Pregnancy, parity and health outcomes beyond breast cancer: potential impact on chronic diseases and other cancer types ». Auditoriet er åpent for publikum. Prøveforelesningen vil også bli strømmet her. The auditorium is open to the public. The defense will still be streamed here. Disputasen starter 11.15 Disputasen will bli strømmet her. The defense will be streamed here. Opptak av disputasen vil være tilgjengelig i et døgn. / A recording of the disputation will be available for 24 hours. De som ønsker å opponere ex auditorio kan sende e-post til leder av disputasen:kajsa.mollersen@uit.no  Opponents’ ex auditorio should sign up to leader of defense by e-mail to:kajsa.mollersen@uit.no

Populærvitenskapelig sammendrag av avhandling

The incidence and prevalence of breast cancer (BC) are increasing worldwide. The reasons for this trend are partly unknown. BC has several well documented modifiable and non-modifiable risk factors. The only known, natural protective factors are breastfeeding and parity. The current paradigm is that the protective effect of parity is mediated by permanent genomic changes in a woman’s breast tissue during her first pregnancy. Many gene expression studies examining breast carcinogenesis, have used a variety of non-cancerous, but not truly normal samples of breast tissue as controls. We performed a series of studies with a systems epidemiology approach to explore association between breast cancer and parity in a postmenopausal population.

The NOWAC study is a prospective national cohort study of 172 000 Norwegian women included between 1991 and 2007. Data is collected from questionnaires and linked national registries.

We found that the women in the Norwegian Women and Cancer Study had a decreasing cumulative incidence rate (CIR) of BC of 0.8% per child, rather than only for the first child. This finding was consistent irrespective of other risk factors and is in line with past studies.

We performed two gene expression studies using microarray technology in order to explore the biological processes underlying this protective effect. To ensure the best possible source of normal tissue, we collected breast tissue samples of 400 healthy postmenopausal women from the same NOWAC cohort. Gene expression profiles of 311 of these samples showed no genomic changes associated with parity, although we did find genomic changes associated with obesity, smoking and alcohol.

Next, we performed a nested case control study of 311 pairs of the same healthy cohort and women with breast cancer in the NOWAC study. We found no impact of parity on global gene expression levels in either cohort.

In conclusion we find that parity is a protective factor for BC for each additional child, not only the first full term pregnancy. However, we find no evidence that parity is associated with permanent genomic changes in normal breast tissue or breast cancer tissue.

Hovedveileder
Professor Ruth Paulssen, Institutt for klinisk medisin, UiT Norges arktiske universitet.

Biveiledere
Professor Emeritus Eiliv Lund, Institutt for samfunnsmedisin, UiT Norges arktiske universitet.

Bedømmelseskomité
Ph.d. Reneé Turzanski Fortner, Kreftregisteret- 1. opponent.
Ph.d. Valerie McCormack, International Agency for Research on Cancer- 2. opponent.
Professor Inigo Martinez, Institutt for klinisk medisin, UiT Norges arktiske universitet – leder av komité.

Disputasleder:

Førsteamanuensis Kajsa Møllersen, UiT Norges arktiske universitet.