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BACKGROUND Phyllodes tumours (PTs) are fibroepithelial breast tumours, which can be classified as benign, borderline or malignant, according to their histological characteristics. While various huge borderline or malignant PTs have been previously described, a benign PT with a pulmonary nodule mimicking malignancy has not yet been reported. In order that doctors may have a comprehensive understanding of super-giant benign PTs (≥ 20 cm), we also performed a literature review to summarize the clinical features, differential diagnosis, and treatment of this disease. CASE SUMMARY A 42-year-old woman with severe anaemia presented with a rapidly enlarging right breast mass, measuring approximately 30 cm × 25 cm × 20 cm that was first noticed 1 year previously. A region of skin ulceration and necrosis (20 cm × 15 cm) was observed on the lateral side of the mass. Computed tomography (CT) of the chest revealed a pulmonary nodule, which initially suggested a diagnosis of metastasis. CT showed that the boundaries between the pectoralis major and the mass were blurred, which was presumed to be due to tumour invasion. However, two core needle biopsies of the mass showed no evidence of malignancy. Following these results, the tumour was removed by mastectomy of the right breast. Interestingly, postoperative pathology finally proved the diagnosis of a benign PT. After 1 year of follow-up, wedge resection of the small pulmonary nodule was performed, and it was confirmed that the lung nodule was actually adenocarcinoma rather than metastatic breast cancer. The patient recovered very well without any postoperative treatment. CONCLUSION This case is unique in that the giant breast mass initially mimicking a malignant clinical presentation was eventually pathologically confirmed to be a benign PT, which misled the diagnosis and complemented the atypical features of benign PTs. The pathological and immunohistochemical results were important in the differential diagnosis. In addition, total mastectomy should be recommended due to difficulty in the precise diagnosis of PTs, especially in large breast masses. In the literature, almost one-half of super-giant benign cases were thought to be malignant tumours before surgery. This finding is a reminder to consider all conditions in order to make an accurate diagnosis and avoid excessive treatment.