Mediterranean Diet and Inequality in Early Breast Cancer

STUDY PURPOSE The project investigates whether adherence to the Mediterranean diet can influence the microbiome, improve quality of life, overall well-being, sense of empowerment, personal feeling of agency, immune activity, levels of short-chain fatty acids and patient outcomes in breast cancer patients undergoing chemotherapy. Additionally, it examines if these effects are more pronounced in individuals with challenging socioeconomic determinants.

BREAST CANCER Among women, breast cancer is the most diagnosed cancer, and is the leading cause of cancer deaths globally in most countries, with 2.3 million new cases recorded in 2022 and approximately 665,000 deaths. In Denmark, there are 5000 new cases, and 1.050 deaths annually, of those 250 in the Region of Southern Denmark. In men, breast cancer is rare with an average of 42 new cases annually in Denmark.

ONCOLOGICAL TREATMENT The oncological treatment of early breast cancer encompasses neoadjuvant (pre-surgery) and adjuvant (post-surgery) treatments.Chemotherapy comprising anthracyclines and taxanes is a cornerstone in both neoadjuvant and adjuvant settings for breast cancer treatment. These drugs have been shown to significantly improve patient outcomes as these regimens are particularly effective in shrinking tumors before surgery, reducing the risk of recurrence and improving overall survival. HER2-targeted therapies, such as trastuzumab, are specifically used for HER2-positive breast cancers in conjunction with chemotherapy and have significantly improved outcomes. Recently, checkpoint immunotherapy, pembrolizumab, has been approved in Denmark for triple-negative early breast cancer together with chemotherapy due to increased pathological complete response (pCR).

SOCIOECONIC INEQUALITY At the national level, disparities in breast cancer outcomes are commonly observed along socioeconomic and demographic lines in both low-, middle- and, high-income countries. These disparities are evident across all stages of the breast cancer continuum, from exposure to modifiable risk factors to access to palliative care and mortality rates. Consequently, women with lower socioeconomic status are more likely to present with late-stage cancer and experience poorer breast cancer prognoses compared to those with higher socioeconomic status. Cancer inequalities at the individual level are predominantly shaped by systemic social determinants of health.

In Denmark an estimated 21% of breast cancer deaths five years after the diagnosis of breast cancer could have been avoided, had patients in all income groups had the same survival rate as the high-income group. Thus, social inequality in cancer survival is a critical problem, and patients with little education, low income, or living alone have poorer survival than better educated cancer patients, with higher income, and living in a relationship. This applies despite women with higher socioeconomic status having significantly higher breast cancer incidence.

GUT MICROBIOTA AND MEDITERRANEAN DIET The human gut hosts approximately 38 trillion cells called the microbiota; the human gut microbiome consists of the genes these cells harbor.

In the 2022 update of Hallmarks of Cancer, the microbiome was introduced as a new important hallmark of cancer. Importantly, the microbiome modulates four other hallmarks: tumor growth, tumor-promoting inflammation, immune evasions, and genomic instability; additionally, the microbiome modulates therapy resistance. The implication is, therefore, that the microbiome is a critical link in cancer development, progression, and treatment response.

The Mediterranean diet is defined as the consumption of fresh fruits, vegetables, nuts, berries, legumes, and non-refined cereals. Olive oil is the principal source of lipids. Moderate intake of alcohol, preferably red wine, with meals; moderate consumption of fish, poultry, eggs, low-fat dairy products, and sweets; monthly consumption of red meat; and regular physical activity.

As the Mediterranean diet includes a wide variety of plant foods and proteins from animal sources, it is a flexible option for many patients. It is not restrictive and allows for many different types of food, with the main limitation being processed foods. This flexibility was a key reason why Harvey et al. chose this diet for a randomized clinical trial involving cancer patients. The study aimed to measure fatigue during chemotherapy and included a sub-study to qualitatively assess how patients felt about making dietary changes during their treatment, identifying facilitators and barriers. Importantly, patients reported that the diet gave them a sense of control and empowerment. They enjoyed learning about nutrition, trying new foods, feeling in control, setting goals, doing something constructive to aid their treatment, and having a positive focus. Barriers included chemotherapy side effects (mouth sores, taste changes, and lack of energy) and food preferences.

Higher adherence to the Mediterranean diet was associated with a 23% lower risk of all-cause mortality. The Mediterranean diet was feasible and safe for adults with cancer. Mediterranean diet has been associated with a reduced risk of breast cancer development. Its impact on survival outcomes after breast cancer diagnosis remains an area of active investigation. Changes in the microbiome composition were observed already after four weeks of the Mediterranean diet.

The Mediterranean diet has several effects, including lipid-lowering and anti-inflammatory actions, reducing chronic inflammation. Moreover, bacteria in the gut ferment dietary fiber to short-chain fatty acids; factors that upregulate immune functions. Short-chain fatty acids are important as an energy source for intestinal epithelial cells, but some enter the bloodstream and act as signaling molecules. They target G-protein-coupled receptors (GPCR) GPCR41, GPCR43, and GPCR109A.

Several studies in patients with melanoma, and cancers of the kidney, lung, and bladder have found that bacterial diversity at baseline can predict response to immunotherapy treatment; some types of bacteria are often reported to be found in larger quantities at baseline in responders than in non-responders, especially Akkermansia mucinifila, Ruminococcaceae, Faecalibacterium, and Lachnospiraceae.

In patients with primary HER2-positive breast cancer undergoing trastuzumab treatment, a recent study revealed the direct involvement of the gut microbiota in trastuzumab efficacy. To the extend of our knowledge, the association with response to checkpoint immunotherapy in breast cancer patients has not been reported.

MICROBIOME AND VITAMIN D Vitamin D has recently been associated with changes in the microbiome and cancer outcomes. Vitamin D is the only vitamin not normally consumed sufficiently even in a well-balanced diet. The main source of vitamin D is solar exposure to the skin. Denmark is situated between the 55th and 57th northern latitudes and therefore UV exposure is insufficient for vitamin D production for large parts of the year. Measurements of vitamin D will be performed at baseline and at Day 1 of cycle 6, and daily supplementation with 50 micrograms of vitamin D is encouraged.

POTENTIAL BENEFITS AND RISKS The potential benefits are that the Mediterranean diet will result in greater microbial diversity during (neo)adjuvant therapy, increase the amounts of short-chain fatty acids in serum and stool, activate the immune system, and improve patient outcomes.

Moreover, the Mediterranean diet may positively impact the patient's social quality of life, overall well-being, sense of empowerment, and personal feeling of agency.

Additionally, these effects may be more pronounced in individuals with challenging socioeconomic determinants.

The potential risk of harm is considered minimal since the intervention is food, and the investigated Mediterranean Diet is comparable to the diet recommended by the Danish Health Authorities (foedevarestyrelsen.dk) The study will be carried out according to the principles outlined in the Declaration of Helsinki. With food as the intervention, the study does not need monitoring from the GCP unit, according to Danish rules.

INTERVENTION The intervention is the Mediterranean Diet.

STUDY POPULATION The study population consists of patients with newly diagnosed early breast cancer, candidates for (neo)adjuvant chemotherapy-based treatment at one of the participating sites in the Region of Southern Denmark.

PATIENT INVOLVEMENT A patient panel, comprising four breast cancer survivors and one representative from a cancer patient association, is actively involved in the design and execution of the MEDITERRACARE study helping developping patient information material, review and provide feedback on questionnaires, and offer practical insights for conducting the trial.

RELEVANCE OF THE TRIAL Changes in bacterial composition can occur within a few weeks of switching to a diet rich in dietary fiber and various plant foods. A positive correlation between gut microbiota and favorable outcomes to checkpoint immunotherapy has been demonstrated in cancer patients. Gut microbiota is important for HER2+ therapy efficacy.

Socioeconomic inequalities are critical for breast cancer patients. The study will evaluate whether adherence to the Mediterranean diet can influence the microbiome, and improve quality of life, overall well-being, sense of empowerment, personal feeling of agency, immune activity, amounts of short-chain fatty acids, and patient outcomes in breast cancer patients undergoing chemotherapy. Additionally, it examines if these effects are more pronounced in individuals with challenging socioeconomic determinants.

This study addresses a knowledge gap. No study worldwide has assessed the Mediterranean diet in early breast cancer patients during chemotherapy with special emphasis on socioeconomic inequality.

HYPOTHESIS The hypothesis is that the Mediterranean diet results in greater microbial diversity during (neo)adjuvant therapy, increases the amounts of short-chain fatty acids in serum and stool, increases the numbers of T- and Natural Killer cells in blood and tumor tissue, reduces inflammation in blood and tumor tissue, and improves patient outcomes.

Moreover, the Mediterranean diet will positively impact the patient's social quality of life, overall well-being, sense of empowerment, and personal feeling of agency.

Additionally, these effects will be more pronounced in individuals with challenging socioeconomic determinants.

STUDY DESIGN The MEDITERRACARE study is designed as a phase II randomized, controlled trial with two arms in a 2:1 allocation ratio evaluating the Mediterranean diet versus regular diet, and a primary endpoint of changes in gut microbiota composition. The study protocol is reported following the CONSORT guidelines.

STUDY SETTING AND RECRUITEMENT Enrolment takes place at four Danish oncology outpatient clinics in the Region of Southern Denmark (Odense, Vejle, Sønderborg, Esbjerg).

Randomization will be performed as block randomization with 2:1 allocation using a computer-generated table of block sizes of 6 or 9, created and supervised by a data manager at OPEN, Open Patient Data Explorative Network, Odense University Hospital, Region of Southern Denmark.

Blinding of patients and health care professionals involved is not intended.

DETAILS ON INTERVENTION The patients randomized to the intervention arm, and if possible a partner or other family member, will receive nutritional guidance during the weekly outpatient chemotherapy visits or via online calls or home visits. Initially 1x weekly during the first month and every other week onwards. In addition, patients will get a booklet on how to implement the Mediterranean Diet in daily life, and access to a password-protected website with teaching videos and Mediterranean diet recipes. To ensure compliance regarding sampling of feces

• Change in alpha diversity in stool samples [Срок оценки: Baseline to Day 1 of chemotherapy cycle 6. Each cycle is 3 weeks for regular schedule or 2 weeks for accelerated schedule, as per clinician decision.]
• Change in beta diversity in stool samples [Срок оценки: Baseline to Day 1 of chemotherapy cycle 6. Each cycle is 3 weeks for regular schedule or 2 weeks for accelerated schedule, as per clinician decision.]
• Level of short-chain fatty acids in stool and plasma [Срок оценки: Baseline to Day 1 of chemotherapy cycle 6. Each cycle is 3 weeks for regular schedule or 2 weeks for accelerated schedule, as per clinician decision.]
• Quality of life measured by WHOQOL-questionnaire [Срок оценки: Baseline to Day 1 of chemotherapy cycle 6. Each cycle is 3 weeks for regular schedule or 2 weeks for accelerated schedule, as per clinician decision.]
• Socioeconomic factors and quality of life correlated with microbiome composition and diversity [Срок оценки: Baseline to Day 1 of chemotherapy cycle 6. Each cycle is 3 weeks for regular schedule or 2 weeks for accelerated schedule, as per clinician decision.]
• Invasive disease-free survival (IDFS) [Срок оценки: From enrollment in study and follow up for 10 years.]
• Distant recurrence-free survival [Срок оценки: From enrollment in study and follow up for 10 years.]
• Overall survival (OS) [Срок оценки: From enrollment in study and follow up for 10 years.]
• Rate of pathological response [Срок оценки: Baseline to date of surgery in neoadjuvant patients.]