Soy Isoflavones for Breast Cancer
For breast cancer, the evidence does not show that soy isoflavones treat or prevent the disease, but it does overturn the old fear that dietary soy is dangerous: at food-level intakes, soy is safe and may even be linked to modestly lower recurrence and mortality. High-dose concentrated isoflavone supplements are a separate question with far weaker safety data, which is why regulators and the grade stay cautious.
Why this grade7-layer evidence engine
This lands at a B "preliminary, disputed" grade because the underlying question is about safety, not cure, and the high-quality evidence is consistent but observational. Large prospective cohorts and pooled analyses align: the Shanghai survivor study (PMID 19996398) found highest-versus-lowest soy intake gave a recurrence HR of 0.68 and total-mortality HR of 0.71; a US-Chinese pooled analysis (PMID 22648714) tied >=10 mg isoflavones/day to recurrence HR 0.75; and meta-analyses (PMID 30382332, 37943034) report overall-survival HR 0.84 and recurrence HR ~0.81. No randomized trials exist for these endpoints, so residual confounding keeps confidence moderate.
The "disputed" status reflects a genuine cross-jurisdiction split rather than contradictory data. EFSA rejected all isoflavone health claims, and the UK NHS states complementary and herbal products are "not recommended" and can interact with other medicines; FDA and Taiwan's TFDA also flag supplements for hormone-sensitive groups. Yet clinical bodies like the Mayo Clinic say soy after a breast cancer diagnosis "improves breast cancer outcomes." The conflict is real but largely about concentrated supplements versus food.
The decisive nuance: every supportive study used dietary soy (tofu, soy milk, edamame), and earlier estrogenicity fears collapsed at these doses, with the LACE cohort (PMID 19221874) showing a protective trend even among tamoxifen users (HR 0.48). The protective signal is strongest in Asian populations (incidence RR 0.76 vs a non-significant 0.97 in Western groups; PMID 21113655). High-dose isoflavone supplements lack comparable safety data, so patients on endocrine therapy should consult their oncologist before using them.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.743
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (1 positive vs 1 negative)，由 raw_score 決定
- tier_strict_requirement_check — | A→B 因 L4 有 ≥1 against
- detect_disputes — 偵測到 1 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status