Kaneyasu Y, Fujiwara H, Akita T, Tanaka J, Shibata Y, Nakagawa T,2025 et al. Suppressive effect of vitamin K2 (menatetrenone) against bone mineral density loss after radiotherapy in uterine cancer patients.

Overview

This lecture reviews a study on whether vitamin K2 (menatetrenone) can suppress bone mineral density (BMD) loss after radiotherapy in uterine cancer patients, with implications for preventing fractures and osteoporosis.

Background & Rationale

• Radiotherapy (RT) in gynecologic cancer increases risk of insufficiency fractures (IFs) due to BMD loss.
• Risk factors for RT-induced fractures include older age, low BMI, multiple pregnancies, low BMD, and postmenopausal status.
• Vitamin K2 is known to support bone health by promoting osteoblast activity and inhibiting bone resorption.

Study Design

• Retrospective study with 34 uterine cancer patients receiving pelvic RT from 2001–2010.
• Group A (n=18) received oral vitamin K2 (45 mg/day for ≥1 year); Group B (n=16) did not.
• BMD measured at L3-L4 (outside RT field) and L5-S1 (inside RT field) pre-RT and multiple timepoints up to 1 year post-RT.

Key Findings

• No significant BMD changes in L3-L4 (non-irradiated region) in either group post-RT.
• Significant BMD loss at L5-S1 (irradiated region) at 6 months post-RT in the non-vitamin K2 group (Group B); no significant loss in vitamin K2 group (Group A).
• Two cases of insufficiency fractures occurred in each group within the radiation field, but vitamin K2 group had no fractures outside irradiation field.
• Patients who developed fractures had lower baseline BMD pre-RT.
• Vitamin K2 was well tolerated; only one case of mild stomatitis was reported.

Discussion & Implications

• Vitamin K2 can suppress RT-induced BMD loss in irradiated pelvic bones but may not fully prevent fractures in high-risk patients.
• Fracture risk after RT is multifactorial; vitamin K2 addresses bone metabolism, not vascular or structural damage from RT.
• Combination therapy with vitamin D3, calcium, and lifestyle interventions may further help at-risk patients.
• Limitations include small sample size, single-center design, and self-selection for vitamin K2.

Key Terms & Definitions

• Bone Mineral Density (BMD) — a measurement indicating bone strength and risk for fractures.
• Insufficiency Fracture (IF) — fracture due to weakened bone, often post-RT.
• Radiotherapy (RT) — cancer treatment using ionizing radiation.
• Vitamin K2 (menatetrenone) — a vitamin form aiding bone metabolism, given orally in this study.
• Osteoblast — bone-forming cell.
• Osteoclast — bone-resorbing cell.

Action Items / Next Steps

• Review combined approaches (vitamin K2, vitamin D3, calcium) for further BMD protection.
• Read about RT effects on bone (focus on fracture risk and prevention).
• Monitor BMD in patients receiving pelvic RT and consider prophylactic interventions in high-risk groups.
• Await further research with larger samples and longer follow-up.