The aim of this pilot study is to assess the change in pain, measured with the Modified Brief Pain Inventory - Short Form (mBPI-sf), at 4, 8, and 12 weeks. The collagen- and chondroitin sulfate-based food supplement may help improve pain in these patients with musculoskeletal symptoms associated with hormone therapy in ER- and/or PR-positive breast cancer.

ER- and/or PR-positive breast cancer is treated with hormone therapy. There is a relationship between the administration of hormone therapy and the presence and/or exacerbation of joint pain in patients with breast cancer.

The administration of food supplement may result in an improvement of pain, as measured by the mBPI-sf questionnaire, in patients undergoing treatment with Aromatase Inhibitors.

Inclusion Criteria:

• Women with histologically confirmed hormone receptor-positive breast carcinoma, without evidence of metastatic disease (M0).
• Surgical treatment completed and any surgery-related complications resolved.
• Currently receiving hormonal therapy with aromatase inhibitors (AIs) for at least 21 days, with pain symptoms lasting less than 6 months attributable to AIs, and with a treatment plan to continue for at least an additional 180 days (6 months).
• Musculoskeletal symptoms associated with hormonal therapy that began or worsened after initiation of such therapy. New musculoskeletal pain must not be specifically due to fractures or traumatic injuries.
• "Average pain" score of at least 4, as assessed by the mBPI-sf questionnaire within 7 days prior to enrollment or baseline visit.
• ECOG performance status of 0-2.
• Patients able to provide informed consent.

Exclusion Criteria:

• Concurrent medical or arthritic conditions that may confound or interfere with the assessment of pain or efficacy, such as rheumatologic/inflammatory arthritis (rheumatoid arthritis, systemic lupus, spondyloarthropathy, psoriatic arthritis, polymyalgia rheumatica) or cancer that may affect bone.
• Chemotherapy and/or radiotherapy completed within 28 days prior to enrollment or baseline visit, and/or unresolved Grade ≥2 side effects related to chemotherapy and/or radiotherapy, except for alopecia and peripheral neuropathy.
• Known allergy or hypersensitivity to Tenflex®.
• Pregnant or breastfeeding patients.