Sense of coherence (SOC) in women treated for breast cancer and its relation to treatment outcome

Breast cancer incidence has, on average increased by 1.4 % annually during the last decades. Early detection and advances in treatment are the main contributing factors for the favourable outcome in terms of five- and ten-year survival rates. The biological factors that influence disease progression and mortality in breast cancer have been well studied. Comparatively less is known about the overall coping ability and their relevance for outcome in the breast cancer-population. The concept of sense of coherence (SOC) reflects a person ́s orientation to life and was established to describe why people remain healthy during times of considerable strain, and manage to make sense out of difficult experiences or situations. In the current thesis SOC is measured by the Sense of Coherence Scale (SOC-13). It contains 13 items that reflects the three core components; comprehensibility, manageability and meaningfulness. Higher SOC scores indicate higher sense of coherence.

The main aim of the thesis was to evaluate the SOC scale's stability and predictive value regarding progression and mortality in breast cancer patients. This was done utilizing a prospective design with a long-term follow-up in a multicenter cohort at four different Swedish hospitals. Two studies were performed. Of the total cohort, 75% and 87% respectively, participated in the two studies.

In paper I, support for the SOC scale ́s stability over time (ICC 0.68, effect size 0.06) was demonstrated. The result of the cross-sectional factor analysis revealed a modified three- factor and a second order factor model meeting criteria for goodness of fit. The longitudinal modified second-order factor model confirmed the construct stability character of the SOC scale with an acceptable goodness-of-fit criteria.

In paper II, patients with high SOC had a 60% lower risk of breast cancer progression and a 80% lower risk of mortality than patients with low SOC over a median follow-up time of 10 years. The mortality risk declined by 2.3% for every one-unit increase in SOC (breast cancer mortality HR, 0.98; 95% CI, 0.96 to 0.99 and all-cause mortality HR, 0.98; 95% CI, 0.96 to 0.99). After adjusting for potential cofounders, the risk declined by 1.7% (breast cancer mortality) and 1.5% (all-cause mortality). The risk of progression declined by 1.4% for every one-unit increase in SOC (HR, 0.99; 95% CI, 0.97 to 1.00). After adjusting for potential cofounders, the decline was 0.7%.

In conclusion, the results from this thesis have shown that the SOC scale and its underlying construct is stable over time when applied to women with breast cancer. In addition, the SOC scale demonstrates a predictive value for disease progression, breast cancer caused mortality and for all-cause mortality among women with breast cancer and can be a valuable instrument for assessment of women at risk.

List of scientific papers

I. Stability of the 13-item sense of coherence (SOC) scale : a longitudinal prospective study in women treated for breast cancer. Lindblad C, Sandelin K, Petersson L-M, Rohani C, Langius-Eklöf A Quality of Life Research (2016) 25:753–760.
https://doi.org/10.1007/s11136-015-1114-4

II. Sense of Coherence (SOC) scale a predictor of survival: a longitudinal prospective study in women treated for breast cancer. Lindblad C, Langius-Eklöf A, Petersson L-M, Sackey H, Bottai M, Sandelin K. [Submitted]