Authors: Farkhanda Gillani , Muhammad Babar Imran , Warda Ahmad , Saira Zafar , Nayyar Rubab , Muhammad Ejaz Khan , Muhammad Shahzad Afzal

Abstract

Background: We report a case of a 54-year-old female patient with carcinoma of the left breast with persistent methylene diphosphonate (MDP) uptake in sclerotic osseous lesions. These lesions were finally declared treated osseous metastatic lesions due to non-avidity on the F18 FDG PET-CT scan, normalization of CA-15.3, and resolution of bone pains. To the best of our knowledge, this has not been reported previously. 
Case presentation:
A 54-year-old woman with persistent backache was referred for further evaluation by a Tc99m MDP bone scan. A Tc-99mmMDP bone scan showed wide-spread skeletal metastatic disease. Magnetic resonance imaging (MRI) showed extensive marrow disease involving the spine and iliac bones. A bone marrow biopsy revealed metastatic carcinoma with a tumor phenotype favoring breast primary. On further workup, the patient was diagnosed with invasive ductal carcinoma of the left breast and was treated with cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors along with hormone therapy and bisphosphonates, followed by radiation therapy for bone metastasis. The skeletal metastatic disease remains static on three consecutive Tc99m MDP bone scans, despite the clinical improvement and decreased tumor marker levels.
The F18-FDG-FDG-CT scan done for monitoring treatment response revealed multiple non-avid sclerotic osseous lesions, favoring treatment response. The patient was continued with the same treatment, and a follow-up Tc99m MDP bone scan after 6 months revealed no interval change in the reported lesions compared to the initial scan. However, a synergistically performed F18 FDG PET-CT scan again showed multiple non-avid sclerotic osseous lesions suggestive of treated metastasis.
Conclusion: This case highlights the importance of 18F-FDG PET-CT in evaluating the treatment response, especially in patients with symptomatic improvement and falling tumor marker levels with static disease on repeated Tc99m MDP bone scans.

Keywords: Tc99m MDP bone scan, breast carcinoma, F18-FDG PET-CT, treated metastasis.