Case Report: We herein report a case of local recurrence of breast cancer with squamous metaplasia and obvious intratumoral and intertumoral heterogeneity. A 39-year-old female patient was diagnosed with T3N2M0 stage IIIB right breast cancer and underwent right total mastectomy and axillar lymph node dissection. At four years after surgery, she became aware of chest wall pain and diagnostic imaging revealed recurrence in the lung, right thoracic wall and sternum. The recurrent lesions remained stable for 18 months with endocrine therapy. Thereafter, the lesion in the right thoracic wall suddenly became enlarged. Moreover, liver metastasis was confirmed on FDG-PET/CT. She underwent right thoracic wall tumor resection. A biopsy was simultaneously performed to obtain a specimen from the site of liver metastasis. Postoperatively, the right chest wall mass showed obvious intratumoral heterogeneity; squamous differentiation with aggressive features and a papillotubular component similar to the primary tumor. The metastatic liver tumor showed similar pathological features to the primary tumor. Conclusion: Intratumoral and intertumoral heterogeneity within primary tumors and associated metastatic sites may contribute to treatment failure and drug resistance.
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