Purpose This scoping review aimed to identify primary studies reporting potentially clinically beneficial interactions between biologically-based complementary medicines (BB-CMs) (e.g., herbs, vitamins, minerals, pre/probiotics etc.) and conventional cancer treatments. Methods Following Joanna Briggs scoping review methodology, a comprehensive search was conducted across Scopus, MEDLINE, Web of Science Core Collection, CINAHL, Allied and Complementary Medicine, and Embase databases from their inception to September 20,2024. Two reviewers independently screened the citations. Data were extracted by a single reviewer and verified by another. Results were tabulated and narrated. Results Fifty-five studies from 14 countries, involving 4,672 adults, adolescents and children, were included in the review. Study designs varied according to the patient characteristics, treatment types, dosages and durations of use, and comprehensiveness of reporting, including adverse events and declarations. Randomized controlled trials (RCTs) (n=29) were most common, followed by non-RCTs (n=9). Studies mostly focused on digestive tract cancers (n=16), breast cancer (n=11) and lung cancer (n=8). The most frequently investigated conventional cancer treatments were chemotherapy (n=17) and chemotherapy with adjunctive medications (n=8), while the most common BB-CMs were traditional medicine multi-ingredient formulations (n=23), vitamins (n=10), and hormone products/pre/probiotics (n=4). The most frequent beneficial interactions evaluated were survival, treatment response, and symptom relief including side effects from conventional cancer treatment, and quality-of-life. Conclusions A broad range of studies have evaluated beneficial interactions between BB-CMs and conventional oncological treatments. Further in-depth reviews of these beneficial interactions, along with more clinical trials are indicated to support evidence-informed decision-making by healthcare providers and people living with cancer.
Between 50 and 85% of patients with solid tumors use dietary supplements following cancer diagnosis, commonly with the intent to boost immune function, alleviate treatment-related toxicities, and improve outcomes. Despite this high prevalence, supplement use is frequently undisclosed to treating oncologists, constraining clinicians’ ability to identify clinically meaningful drug–supplement interactions and provide evidence-based counseling. This review synthesizes available evidence on the efficacy, safety, pharmacological interactions, regulatory framework, and communication strategies relevant to supplement use in solid tumor oncology. Among the supplements reviewed, omega-3 fatty acids demonstrate consistent anti-inflammatory effects and provide modest benefit in cancer cachexia, particularly in gastrointestinal and pancreatic malignancies undergoing active chemotherapy, though evidence supporting improvement in lean body mass is inconsistent. Vitamin D supplementation is established for bone health in patients at risk for deficiency or treatment-related osteoporosis; while observational data suggest a modest reduction in cancer mortality, randomized controlled trials have not confirmed consistent improvements in cancer-specific survival endpoints. Probiotics robustly reduce the incidence and severity of chemotherapy- and radiotherapy-induced diarrhea (NNT 3–5) and show emerging potential for augmenting immune checkpoint inhibitor efficacy, with Akkermansia muciniphila identified as a mechanistically relevant and clinically significant commensal species. Melatonin may improve one-year survival rates and reduce chemotherapy-induced stomatitis, though the quality of evidence remains limited by small trials, heterogeneous populations, and significant risk of bias. Pharmacologically, supplements interact with anticancer agents primarily through cytochrome P450 modulation, P-glycoprotein interference, and pharmacodynamic potentiation of anticoagulant and antiplatelet agents. The regulatory gap created by the Dietary Supplement Health and Education Act (DSHEA) introduces substantial variability in product quality, purity, and safety oversight. Evidence-based integration of supplements into solid tumor care requires systematic screening, individualized risk–benefit assessment, and structured oncologist–patient communication grounded in current clinical evidence.
