Extensive bone metastases from an occult gastric primary: A case report.

Background: This report describes a rare case of a small gastric cancer lesion with widespread bone metastases and markedly elevated alkaline phosphatase levels that was initially misdiagnosed as rheumatoid arthritis, as the patient's sole clinical manifestation was chronic bone pain persisting for 1 year.

Case summary: An 83-year-old man was admitted due to worsening generalized joint pain over 1 year. Serum alkaline phosphatase levels were markedly elevated, and technetium-99m methylene diphosphonate single-photon emission computed tomography (CT) and fluorine-18 sodium fluoride positron emission tomography (PET)/CT images showed symmetrical diffuse uptake of the radiotracers throughout the skeleton. Initially, Paget's disease was suspected, but abnormal hematologic tumor markers and bone biopsy confirmed metastatic adenocarcinoma. Fluorine-18-fluorodeoxyglucose PET/CT did not reveal a primary tumor. The patient had a history of colon polypectomy and tubulovillous adenoma with atypical hyperplasia on pathological examination 10 years prior. Further investigation using gallium-68-labeled fibroblast-activation protein inhibitor PET/CT images showed increased punctate uptake in the gastric antrum. Gastroscopy demonstrated a 1.0 cm ulcerated mass in the prepyloric region, and histopathological evaluation of the biopsy specimen revealed poorly differentiated adenocarcinoma. The incidence of bone metastases from gastric cancer is very low, especially with such extensive involvement.

Conclusion: Occult gastric carcinomas with bone metastases necessitate proactive high-risk surveillance and multidisciplinary integration to improve diagnostic accuracy and clinical outcomes.