CBD and breast cancer: between research, well-being and vigilance (Breast Cancer Awareness Month)

During this Pink October, dedicated to raising awareness and screening for breast cancer, many patients are wondering about supportive approaches and integrative therapies. Among them, the use of cannabidiol (CBD) is attracting growing interest, fueled by preclinical research and a legitimate quest for relief from the side effects of conventional treatments.

However, between therapeutic hopes, the reality of clinical data, and major risks of drug interactions, it is essential to approach the subject with rigor and caution.

1. Where does research on CBD and breast cancer stand?

Promising preclinical leads

Numerous preclinical studies (in vitro and in vivo on animal models) suggest that cannabinoids, and particularly CBD, possess interesting biological properties. Regarding breast cancer specifically—which represents the leading cause of new cases and the second leading cause of cancer death among women in the United States—CBD has demonstrated pro-apoptotic activity (promoting tumor cell death) and anti-proliferative effects.

Some studies also suggest that CBD could act on the tumor environment by reducing inflammation or by inhibiting the development of new blood vessels feeding the tumor. However, these preliminary results obtained in the laboratory cannot constitute proof of clinical efficacy in humans. To date, there is not enough clinical data to recommend CBD as an anti-cancer treatment.

Managing symptoms and anti-hormonal therapies

Adjuvant treatments, such as anti-hormonal therapy (aromatase inhibitors like letrozole, anastrozole, or tamoxifen), cause frequent side effects that heavily impact patients' quality of life:

• Musculoskeletal and joint symptoms: Affecting more than 46% of patients on hormone therapy.
• Hot flashes and vasomotor symptoms: Affecting more than 95% of them.
• Sleep disorders, anxiety, and chronic fatigue.

According to surveys conducted among patients, a significant proportion (between 20% and 40%) have used or currently use cannabis-based products to try to alleviate these daily burdens (pain, insomnia, anxiety). Nevertheless, evidence remains fragmented and requires strict medical supervision.

2. The critical risk: drug interactions

This is the absolute point of vigilance highlighted by oncologists and hospital pharmacists (as noted by Prof. Gisèle Chvetzoff of the Centre Léon Bérard).

The complex role of hepatic metabolism

CBD is metabolized by the liver via the cytochrome P450 enzyme system (notably the CYP3A4 and CYP2D6 enzymes). Yet, the vast majority of anti-cancer treatments and anti-hormonal therapies use exactly the same metabolic pathways.

• Risk of overdose or underdose: CBD can act as an enzyme inhibitor. By changing the speed at which drugs are eliminated, it risks increasing the toxicity of cancer treatments or, conversely, reducing their therapeutic effectiveness (as has been documented for active metabolites of tamoxifen, such as endoxifen).
• Caution with natural health products: Similar interactions are observed with other substances such as melatonin.

This is why oncology teams strongly advise against self-medication with CBD during active cancer treatment (chemotherapy, targeted therapies, hormone therapy), except within the strict framework of palliative care protocols or under direct medical supervision.

3. What is the place for validated integrative approaches?

While the use of therapeutic cannabis or over-the-counter CBD is subject to reservations during treatment due to interactions, scholarly societies in integrative oncology (such as the Society for Integrative Oncology and ASCO) validate and recommend other non-pharmacological approaches to relieve patients:

• Acupuncture: Recommended by ASCO to significantly reduce hot flashes and joint pain associated with aromatase inhibitors.
• Yoga and mindfulness meditation: Effective for reducing anxiety, improving sleep quality, and supporting patients' emotional balance.
• Adapted physical activity: An essential pillar of care to limit fatigue and preserve bone health.

4. Practical recommendations and the caregiver-patient dialogue

As part of Pink October, the paramount message is one of transparency and safety:

• Do not remain isolated: If you are considering using hemp or CBD-based products to soothe certain discomforts, talk about it openly with your oncologist, your pivot nurse, or your clinical pharmacist.
• Break the taboo: Medical teams are increasingly trained to listen to complementary medicine. The fear of being judged should not lead you to hide the use of natural substances that could interact with your medications.
• Check quality and legality: If external comfort use is validated by your medical team (such as topical CBD cosmetic products to locally relax a muscle area outside of active treatment), be sure to choose compliant products that display a THC rate of less than 0.3% and feature rigorous analysis certificates.