Incidence of breast cancer subtypes in immigrant and non-immigrant women in Norway.

BACKGROUND: Breast cancer incidence differs between non-immigrants and immigrants from low- and middle-income countries. This study investigates whether immigrants also have different subtype-specific incidences. METHODS: We used national health registries in Norway and calculated subtype-specific incidence rate ratios (IRRs) for invasive breast cancer among women aged 20-75 and 20-49 years between 2005 and 2015. Immigrant groups were classified by country of birth broadly defined based on WHO regional groupings. Subtype was defined using estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor 2 (HER2) status as luminal A-like (ER+ PR+ HER2-), luminal B-like/HER2- (ER+ PR- HER2-), luminal B-like/HER2+ (ER+ PR any HER2+), HER2+ (ER-PR-HER2+) and triple-negative breast cancer (TNBC) (ER-PR-HER2-). RESULTS: Compared to non-immigrants, incidence of the luminal A-like subtype was lower in immigrants from Sub-Saharan Africa (IRR 0.43 95% CI 0.28-0.66), South East Asia (IRR 0.63 95% CI 0.51-0.79), South Asia (IRR 0.67 95% CI 0.52-0.86) and Eastern Europe (IRR 0.86 95% CI 0.76-0.99). Immigrants from South Asia had higher rates of HER2 + tumors (IRR 2.02 95% CI 1.26-3.23). The rates of TNBC tended to be similar regardless of region of birth, except that women from South East Asia had an IRR of 0.54 (95% CI 0.32-0.91). CONCLUSIONS: Women from Eastern Europe, Sub-Saharan Africa and Asia had different subtype-specific incidences compared to women from high-income countries (including non-immigrants). These differences in tumor characteristics between immigrant groups should be taken into consideration when planning preventive or screening strategies.

In modern times, how important are breast cancer stage, grade and receptor subtype for survival: a population-based cohort study.

BACKGROUND: In breast cancer, immunohistochemistry (IHC) subtypes, together with grade and stage, are well-known independent predictors of breast cancer death. Given the immense changes in breast cancer treatment and survival over time, we used recent population-based data to test the combined influence of IHC subtypes, grade and stage on breast cancer death. METHODS: We identified 24,137 women with invasive breast cancer aged 20 to 74 between 2005 and 2015 in the database of the Cancer Registry of Norway. Kaplan-Meier curves, mortality rates and adjusted hazard ratios for breast cancer death were estimated by IHC subtypes, grade, tumour size and nodal status during 13 years of follow-up. RESULTS: Within all IHC subtypes, grade, tumour size and nodal status were independent predictors of breast cancer death. When combining all prognostic factors, the risk of death was 20- to 40-fold higher in the worst groups compared to the group with the smallest size, low grade and ER+PR+HER2- status. Among node-negative ER+HER2- tumours, larger size conferred a significantly increased breast cancer mortality. ER+PR-HER2- tumours of high grade and advanced stage showed particularly high breast cancer mortality similar to TNBC. When examining early versus late mortality, grade, size and nodal status explained most of the late (> 5 years) mortality among ER+ subtypes. CONCLUSIONS: There is a wide range of risks of dying from breast cancer, also across small breast tumours of low/intermediate grade, and among node-negative tumours. Thus, even with modern breast cancer treatment, stage, grade and molecular subtype (reflected by IHC subtypes) matter for prognosis.

Breast cancer-specific survival by clinical subtype after 7 years follow-up of young and elderly women in a nationwide cohort.

Age and tumor subtype are prognostic factors for breast cancer survival, but it is unclear which matters the most. We used population-based data to address this question. We identified 21,384 women diagnosed with breast cancer at ages 20-89 between 2005 and 2015 in the Cancer Registry of Norway. Subtype was defined using estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor 2 (HER2) status as luminal A-like (ER+PR+HER2-), luminal B-like HER2-negative (ER+PR-HER2-), luminal B-like HER2-positive (ER+PR+/-HER2+), HER2-positive (ER-PR-HER2+) and triple-negative (TNBC) (ER-PR-HER2-). Cox regression estimated hazard ratios (HR) for breast cancer-specific 7-year survival by age and subtype, while adjusting for year, grade, TNM stage and treatment. Young women more often had HER2-positive and TNBC tumors, while elderly women (70-89) more often had luminal A-like tumors. Compared to age 50-59, young women had doubled breast cancer-specific mortality rate (HR = 2.26, 95% CI 1.81-2.82), while elderly had two to five times higher mortality rate (70-79: HR = 2.25, 1.87-2.71; 80-89: HR = 5.19, 4.21-6.41). After adjustments, the association was non-significant among young women but remained high among elderly. Young age was associated with increased breast cancer-specific mortality among luminal A-like subtype, while old age was associated with increased mortality in all subtypes. Age and subtype were strong independent prognostic factors. The elderly always did worse, also after adjustment for subtype. Tumor-associated factors (subtype, grade and stage) largely explained the higher breast cancer-specific mortality among young. Future studies should address why luminal A-like subtype is associated with a higher mortality rate in young women.

Changing patterns of breast cancer incidence and mortality by education level over four decades in Norway, 1971-2009.

Background: In the last century, breast cancer incidence and mortality was higher among higher versus lower educated women in developed countries. Post-millennium, incidence rates have flattened off and mortality declined. We examined breast cancer trends by education level, to see whether recent improvements in incidence and mortality rates have occurred in all education groups. Methods: We linked individual registry data on female Norwegian inhabitants aged 35 years and over during 1971­2009. Using Poisson models, we calculated absolute and relative educational differences in age-standardised breast cancer incidence and mortality over four decades. We estimated educational differences by Slope and Relative Index of Inequality, which correspond to rate difference and rate ratio, comparing the highest to lowest educated women. Results: Pre-millennium, incidence and mortality of breast cancer were significantly higher in higher versus lower educated women. Post-millennium, educational differences in breast cancer incidence and mortality attenuated. During 2000­2009, breast cancer incidence was still 38% higher for higher versus lower educated women (Relative Index of Inequality: 1.38, 95% confidence interval: 1.31­1.44), but mortality no longer varied significantly by education level (Relative Index of Inequality: 1.09, 95% confidence interval: 0.99­1.19). Among women below 50 years, however, the education gradient for mortality reversed, and mortality was 28% lower for the highest versus lowest educated women during 2000­2009 (Relative Index of Inequality: 0.72, 95% confidence interval: 0.51­0.93). Results: Post-millennium improvements in breast cancer incidence and mortality have primarily benefited higher educated women. Breast cancer mortality is now highest among the lowest educated women below 50 years.