IntroductionPhyllodes tumors account for less than 1% of breast tumors in women, and giant phyllodes tumors are those that are larger than 10 cm in diameter. Removal of such large tumors places a huge burden on the surgeon to reconstruct a breast that is aesthetically acceptable by the patient. We report what may be the largest giant phyllodes tumor and, most likely, the first latissimus dorsi flap used to cover such a large defect caused by the resection.Case presentationWe report the case of a 36-year-old Malaysian woman who presented with a three-year history of gradually increasing swelling of the left breast, with skin changes. Examination revealed a huge, globular, lobulated mass measuring 400 mm by 350 mm. The patient had a mastectomy with an immediate latissimus dorsi pedicled myocutaneous flap reconstruction. The breast weighed 8.27 kg, and ex vivo, the tumor measured 280 mm by 250 mm by 180 mm. Histopathologic analysis confirmed the diagnosis as a giant phyllodes tumor. At 12-month follow-up, the patient reports no complications and is satisfied with the aesthetic outcome.ConclusionGiant phyllodes tumors are very rare tumors that can reach up to 40 cm in diameter. Reconstruction of such a defect is a great challenge, and we report what we believe is the first latissimus dorsi flap to cover successfully a defect of approximately 400 mm by 350 mm.