pregnancy and breast cancer

104 Pages·2016·1.13 MB·English

From the DEPARTMENT OF
MEDICAL EPIDEMIOLOGY AND BIOSTATISTICS
Karolinska Institutet, Stockholm, Sweden
PREGNANCY AND BREAST CANCER:
RISK PATTERNS, TUMOUR
CHARACTERISTICS AND PROGNOSIS
Anna L.V. Johansson

Stockholm 2016
All previously published papers were reproduced with permission from the publisher.
Cover photo: Anna L.V. Johansson/Robert Karlsson (front), Peter Weibull (back)
Published by Karolinska Institutet.
Printed by Eprint AB 2016
© Anna L.V. Johansson, 2016
ISBN 978-91-7676-191-5
Institutionen för medicinsk epidemiologi och biostatistik

Pregnancy and breast cancer:
Risk patterns, tumour characteristics
and prognosis

AKADEMISK AVHANDLING

som för avläggande av medicine doktorsexamen vid Karolinska Institutet offentligen
försvaras i hörsal Andreas Vesalius, Berzelius väg 3, Karolinska Institutet, Solna
Fredagen den 8 april 2016, kl 09.00
av
Anna L.V. Johansson
Huvudhandledare: Opponent:
Professor Mats Lambe Professor Giske Ursin
Karolinska Institutet University of Oslo, Norway
Institutionen för medicinsk epidemiologi och Institute of Basic Medical Sciences
biostatistik Department of Nutrition
Division of Cancer and Lifestyle Factors
Bihandledare:
Professor Paul W. Dickman Betygsnämnd:
Karolinska Institutet Professor Anders Ahlbom
Institutionen för medicinsk epidemiologi och Karolinska Institutet
biostatistik Institutet för miljömedicin
Enheten för epidemiologi
Professor Sven Cnattingius
Karolinska Institutet Docent Signe Borgquist
Institutionen för medicin, Solna Lunds universitet
Enheten för klinisk epidemiologi Institutionen för kliniska vetenskaper, Lund
Avd för onkologi och patologi

Professor Max Petzold
Göteborgs universitet
Institutionen för medicin, Sahlgrenska akademin
Avd för samhällsmedicin och folkhälsa

Stockholm 2016

To the women and their families

To Mats, Paul and Sven

ABSTRACT
Pregnancy-associated breast cancer (PABC) is commonly defined as a breast cancer (BC)
diagnosed during pregnancy or within one or two years after delivery. The risk of BC is lower
than expected during pregnancy with a small rebound within 2 years after delivery, compared
to non-pregnant women of the same age. Although a rare event, there is evidence that women
with PABC have a poorer prognosis compared to women with BC diagnosed not near a
pregnancy (non-PABC). It is important to improve the understanding of underlying
mechanisms and identify factors that may influence outcome, including the role of detection
and tumour biology. The possible influence of pregnancy exposures on detection and tumour
biology may be time-varying, with different effects during the pregnancy period compared to
time windows further away from delivery. Since a transient risk has been reported 5-10 years
post-delivery, it is also of interest to compare pregnancy-associated tumours to tumours
diagnosed further away, say up to ten years, from delivery with respect to tumour biology and
prognosis.
Having a relative with breast cancer is an established risk factor for breast cancer, in
particular at a young age. Women with a family history of breast cancer may be more likely
to have pre-malignant breast cells at a young age, and could be more susceptible to
pregnancy-related exposures, such as elevated levels of endogenous hormones. Study III
assessed the risk pattern for breast cancer during pregnancy and up to ten years after delivery
in relation to family history of breast cancer using a cohort of 3.5 million women aged 15-44
years identified in the Swedish Multi-Generation Register and the Swedish Cancer Register.
In total, 15,548 women had a recorded BC diagnosis of which 1,208 were PABC. To reduce
the comparison population and improve computational efficiency, a case-cohort design was
utilised. The results showed that a family history of BC did not affect the risk pattern around
pregnancy and up to 10 years post-delivery, indicating that pregnancy-related exposures do
not interact with the familial pre-disposition for BC in these women.
Results from several studies have suggested that BC tumours diagnosed around delivery have
adverse tumour characteristics, such as advanced TNM stage and triple-negative subtype, but
it remains unclear if adverse tumour characteristics can fully explain the worse prognosis in
women with PABC. Studies II and IV assessed TNM stage in cohorts of patients diagnosed
with BC during pregnancy and up to ten years post-delivery using information from the
Swedish Cancer Register for years 2002-2009 (study II) and the Swedish Breast Cancer
Quality Register for years 1992-2009 (study IV). Study IV also assessed histological grade
and tumour biology, such as hormone receptor status. The results showed that tumours
detected during pregnancy and within one year of delivery were more often advanced, of high
grade and hormone receptor negative (triple-negative and non-luminal Her2 positive
subtypes) compared to nulliparous women. These associations were most pronounced in
tumours diagnosed during the first six months post-delivery. In combination with the
previously observed lower risk during pregnancy, these findings could reflect diagnostic
delays, resulting in more advanced tumours at diagnosis, or a suppression of hormone
responsive tumours around delivery.
With the aim to investigate prognosis in women with PABC, two partly over-lapping cohorts
of BC patients were identified in the Swedish Cancer Register for years 1963-2002 (study I)
and in the Breast Cancer Quality Register for years 1992-2009 (study IV), including 1,110
and 778 women with PABC, respectively. The association between PABC and mortality was
analysed using Cox regression and flexible parametric models. The results from study I and
IV corroborated previous findings that women with PABC have a poorer prognosis compared
to women with non-PABC. The mortality was highest in women diagnosed 0-6 months after
delivery, and remained elevated up to eight years after diagnosis, in comparison to women
diagnosed not near a delivery. However, following adjustment for tumour characteristics, the
difference in mortality between women with PABC and women with non-PABC was
attenuated and non-significant (study IV). These findings suggest that although PABC is
associated with more advanced and aggressive tumours, the outcome is similar to that in
women with non-PABC when taking tumour characteristics into account.
For comparison, we also assessed tumour characteristics and prognosis in women diagnosed
with BC 2-10 years after delivery (study IV). A transient risk of BC around 5-10 years after
delivery has been reported previously. Compared to nulliparous women, women diagnosed 2-
5 years post-delivery did not differ in tumour size, grade and ER status, but more often
presented with spread to lymph nodes, negative PR status and non-luminal Her2 positive
subtype. Women with BC diagnosed 2-5 years post-delivery also exhibited a poorer
prognosis compared to nulliparous women, which remained significant after adjustment for
T/N stage and hormone receptor status. These findings could indicate different mechanisms
for risk, detection and prognosis in women diagnosed 2-5 years after delivery compared to
women with PABC.
In conclusion, the findings indicate that pregnant and lactating women exhibit different
patterns of BC risk, tumour biology and prognosis compared to other pre-menopausal women
with BC. The poorer prognosis observed in women with PABC can largely be explained by
adverse tumour characteristics at diagnosis. The effects of pregnancy appear to persist beyond

2 years after delivery.
LIST OF SCIENTIFIC PAPERS
I. Johansson ALV, Andersson TM-L, Hsieh CC, Cnattingius S, Lambe M.
Increased mortality in women with breast cancer detected during
pregnancy and different periods postpartum. Cancer Epidemiol
Biomarkers Prev. 2011 Sep;20(9):1865-72.

II. Johansson ALV, Andersson TM-L, Hsieh CC, Jirström K, Dickman P,
Cnattingius S, Lambe M. Stage at diagnosis and mortality in women with
pregnancy-associated breast cancer (PABC). Breast Cancer Res Treat.
2013 May;139(1):183-92.

III. Johansson ALV, Andersson TM-L, Hsieh CC, Cnattingius S, Dickman P,
Lambe M. Family history and risk of pregnancy-associated breast cancer
(PABC). Breast Cancer Res Treat. 2015 May;151(1):209-17.

IV. Johansson ALV, Andersson TML, Hsieh CC, Jirström K, Cnattingius S,
Fredriksson I, Dickman P, Lambe M. Tumor characteristics and prognosis
in women with pregnancy-associated breast cancer. In manuscript.
RELATED PUBLICATIONS
(Not included in the thesis)
 Andersson TM-L, Johansson ALV, Hsieh CC, Cnattingius S, Lambe M.
Increasing incidence of pregnancy-associated breast cancer in Sweden.
Obstet Gynecol. 2009 Sep;114(3):568-72.

 Johansson ALV, Andersson TM-L, Plym A, Ullenhag GJ, Møller H, Lambe
M. Mortality in women with pregnancy-associated malignant melanoma.
J Am Acad Dermatol. 2014 Dec;71(6):1093-101.

 Andersson TM-L, Johansson ALV, Fredriksson I, Lambe M. Cancer during
pregnancy and the postpartum period: A population-based study.
Cancer. 2015 Jun;121(12):2072-7.