Proliferation in operable breast cancer : Aspects of prognostication and relevance of carbohydrate metabolism

Abstract

Breast cancer is the most common malignant disease among women in the Western world. In Norway and the Netherlands, the incidence has more than doubled in the last 50 years, likely due to increased estrogen exposure, higher levels of alimentary carbohydrates and fat, and reduced physical activity, the so-called Western lifestyle. Treatment of breast cancer is based on an additive multimodal approach comprising surgery, radiation therapy, and adjuvant systemic therapy (i.e., chemotherapy, anti-estrogen therapy, and biological therapy). However, the disease is heterogeneous with different molecular gene expression profiles, phenotypes, and risk profiles. Thus, it is important to optimize treatment to avoid over- and under-treatment; to achieve this, prognostic and predictive factors must be explored further. The first study is a retrospective population-based study in which we used the original Multicenter Morphometric Mammary Carcinoma Project (MMMCP) data set from the Netherlands and introduced new exposure variables. We compared the prognostic power of tumor proliferation to classical prognostic factors in treatment-naïve patients with lymph node-negative BC aged < 55 years. Several tools are available for clinicians making decisions regarding adjuvant systemic treatment. Among these tools, we used the Norwegian Breast Cancer Group treatment guidelines from 2010 and Adjuvant! Online v 8.0. Compared to the grouping obtained by these tools, MAI-3 identified 40% of the patients as under-treated and 20% of the patients as over-treated, which shows the importance of proliferation as a prognostic and predictive factor that should be included in the decision-making process for treatment. Later, Ki-67 was added to the Norwegian Breast Cancer Group (NBCG) guidelines with changes to the treatment regimen for luminal breast cancer patients. The second study is a randomized controlled trial in which we examined the influence of pre-operative carbohydrate load compared to standard fasting procedures regarding tumor proliferation and clinical outcome in operable breast cancer patients. The Enhanced Recovery After Surgery (ERAS) protocol is used for patients going through major surgery with pre-operative carbohydrate loading. To the best of our knowledge, no studies have explored the effects of such carbohydrate loading in tumor tissue. In our study, we observed an increase in the number of luminal breast cancer patients with MAI≥10 in the group receiving pre-operative carbohydrate load. The proportion of PR-negative patients was also increased in the carbohydrate group. No differences were found regarding the well-being of patients after surgery. Both relapse-free survival (RFS) and breast cancer-specific survival (BCSS) were inferior among the ER+/T2 patients in the carbohydrate group. In the third study, we performed an explorative study based on the patient material from the second study. The metabolic consequences were explored in the tumor and liquid biopsies from operable breast cancer patients receiving pre-operative carbohydrate loading. Pre-operative carbohydrate loading increased the systemic lactate and pyruvate content in patients with high-proliferation tumors. Tumor tissue with high proliferation had high glutathione content, which is an intratumoral protection factor. The metabolic signature or pathway is the same as in the Warburg effect. Regarding microRNA involved in endocrine resistance, four out of seven microRNAs were recruited after carbohydrate loading. High levels of systemic lactate and pyruvate and tissue glutathione were associated with decreased RFS, BCSS, and overall survival (OS). Integrated pathway analysis in serum revealed the activation of five major anabolic metabolic networks contributing to proliferation and growth. These findings agree with previous studies showing that metabolic profiling of serum samples can provide prognostic information in operable breast cancer. Future research comprises the calibration of MAI against the gold standard PAM-50 (Prosigna) test through the nationwide EMIT study endorsed by the NBCG, which has added the Prosigna test to their 2020 treatment guidelines. However, the inexpensive and standardized MAI may serve as a good proxy for costly gene expression methods, especially in developing countries. We also suggest performing a new randomized controlled trial in ER+/T2 patients with a metformin arm, a metformin + endocrine therapy arm and placebo arm. The metformin or metformin + endocrine therapy should be introduced after diagnostic biopsy, but before surgery. Moreover, glutathione should be pursued for the purpose of targeted therapy. The above-mentioned strategies seem to be only a small step for biomarker research but will undoubtedly bring the clinical knowledge regarding the relevance of metabolic networks a giant leap forward.