Comorbid chronic diseases affect cancer patients with an increasing frequency as populations get older. They affect underserved populations more so than the affluent. Recent surveys in South Africa showed that many cancer patients experience at least one comorbidity. Co-infections involving different viruses, or the combination of viruses and bacterial infections are particularly common in low-income countries and lead to a weakened immune system and chronic inflammation in affected individuals which are both predispositions for cancer. Comorbidities like diabetes, chronic cardiovascular, liver and renal diseases, autoimmune diseases and chronic stress are well known to modify cancer risk and negatively affect cancer outcomes. Notably, co-morbidities and cancer have common risk factors. Recent data have shown that many of these co-morbidities can have a direct influence on the microbiome, the immune response, and tumor biology. Nevertheless, comorbidities are frequently ignored in the decision process of how cancer patients are treated. In my overview, we will discuss broadly the influence of co-morbidities on cancer susceptibility, the burden of co-morbidities in cancer patients, and how co-morbidities may influence cancer etiology, biology, and survivorship.

The presence of pre-existing morbidities poses a challenge to cancer patient care. It may delay presentation, affect treatment decisions and outcomes. There is little information on the profile and prevalence of multi-morbidities in breast cancer patients across middle-income countries (MIC) to lower income countries (LIC) in sub-Saharan Africa (SSA).

The African Breast Cancer–Disparities in Outcomes (ABC-DO) breast cancer cohort is a prospective hospital-based study that spans upper MICs South Africa and Namibia, lower MICs Zambia and Nigeria, and LIC Uganda. Seven pre-existing morbidities were assessed at cancer diagnosis: obesity, hypertension, diabetes, asthma/chronic obstructive pulmonary disease, heart disease, tuberculosis, and HIV. Logistic regression models were used to assess determinants of ≥2 of the seven above-mentioned conditions (defined as multimorbidity) and the influence of multimorbidity on advanced stage (stage III/IV) breast cancer diagnosis.


Among 2189 women, morbidity prevalence was the highest for obesity (35%, country-specific range 15-57%), hypertension (32%, 15-51%) and HIV (16%, 2-26%) then for diabetes (7%, 4%-10%), asthma (4%, 2%-10%), tuberculosis (4%, 0%-8%) and heart disease (3%, 1%-7%). Obesity and hypertension were more common in upper MICs and in higher socioeconomic groups. Overall, 27% of women had multimorbidity. Older women were more likely to have obesity (odds ratio: 1.09 per 10 years, 95% CI 1.01-1.18), hypertension (1.98, 1.81-2.17), diabetes (1.51, 1.32-1.74), and heart disease (1.69, 1.37-2.09) and were less likely to be HIV positive (0.64, 0.58-0.71). Multimorbidity was not associated with stage at diagnosis, with the exception of earlier stage in obese and hypertensive women.

Breast cancer patients in higher-income countries and higher social groups in SSA face the additional burden of pre-existing non-communicable diseases, particularly obesity and hypertension, exacerbated by HIV in Southern/Eastern Africa. While HIV is not thought to contribute to breast cancer development, reports suggest that HIV-positive patients have a poorer prognosis.