Partner status and survival after cancer: A competing risks analysis

Highlights

• Partner effect modelled with flexible parametric competing risk survival models.

• Estimated both cause-specific hazards and cumulative probability of death by sex.

• Among 100 unpartnered male cancer patients 58 will die versus 46 for partnered.

• Unpartnered patients face worse cancer-specific and competing mortality.

• Follow-up care should be tailored accordingly for this patient population.

Abstract

Objective

The survival benefits of having a partner for all cancers combined is well recognized, however its prognostic importance for individual cancer types, including competing mortality causes, is less clear. This study was undertaken to quantify the impact of partner status on survival due to cancer-specific and competing mortality causes.

Methods

Data were obtained from the population-based Queensland Cancer Registry on 176,050 incident cases of ten leading cancers diagnosed in Queensland (Australia) from 1996 to 2012. Flexible parametric competing-risks models were used to estimate cause-specific hazards and cumulative probabilities of death, adjusting for age, stage (breast, colorectal and melanoma only) and stratifying by sex.

Results

Both unpartnered males and females had higher total cumulative probability of death than their partnered counterparts for each site. For example, the survival disadvantage for unpartnered males ranged from 3% to 30% with higher mortality burden from both the primary cancer and competing mortality causes. The cause-specific age-adjusted hazard ratios were also consistent with patients without a partner having increased mortality risk although the specific effect varied by site, sex and cause of death. For all combined sites, unpartnered males had a 46%, 18% and 44% higher risk of cancer-specific, other cancer and non-cancer mortality respectively with similar patterns for females. The higher mortality risk persisted after adjustment for stage.

Conclusions

It is important to better understand the mechanisms by which having a partner is beneficial following a cancer diagnosis, so that this can inform improvements in cancer management for all people with cancer.

Introduction

The protective effect of marriage on overall cancer survival [1] has been well established. Emerging evidence also suggests that the survival benefit for married patients may be increasing over time [2]. The protective effect of marriage may reflect increased social support over the cancer continuum from diagnosis to survivorship to buffer the adverse effects of stress-related biological processes and immune responses [1], [3]. Having a partner may also provide a source of financial, practical and emotional support while undergoing treatment and has been linked to more timely care, increased receipt of curative therapies, greater compliance with multi-modal treatments and improved psychosocial outcomes [1], [3], [4], [5], [6], [7], [8], [9].

Results from studies that combine cancer sites may be affected by too much aggregation across different diseases. However findings to date on the impact of being married on cause-specific survival for individual cancer sites are equivocal with non-significant [6], [10], protective [4], [5], [11], [12], [13], [14], [15] and mixed effects [16], [17] being reported after adjusting for various combinations of known survival determinants. Some [4], [12], [16] but not all [15], [18] studies also reported that the partner effect varied by gender. These inconsistencies likely reflect the heterogeneity in time period, cohort characteristic, covariates included in statistical models and definition of marital status across studies. While several categorized patients as married or unmarried based on official marital status categories [4], [5], [13], [14] or extended the married group to also include partnered patients [11], [12], others split the unmarried category into sub-groups (single, widowed, divorced or separated) [6], [15], [16], [17].

The impact of partner status has typically being reported using net survival [4], [10], [12], [15], describing the hypothetical situation where the diagnosed cancer is the only cause of death [19]. In the real world, however patients are at risk of death from various mutually exclusive causes. Hence partitioning overall mortality into different causes has the potential to provide a richer understanding of the impact having a partner has on survival after a cancer diagnosis [20], [21]. To date, only a few studies have reported on the beneficial effects of having a partner on both cancer-specific [5], [22], [23], [24] and competing mortality causes [22], [24], however none have systematically compared these effects across multiple cancer sites. In this study we quantified the survival benefit of being partnered for each of the ten leading cancers diagnosed in Queensland, Australia using population-based data and competing risk methods [21].