Abstract
BACKGROUND: Myofibroblastoma (MFB) and low-grade adenosquamous carcinoma (LGASC) are rare tumours in the breast, respectively. However, a collision tumour of the two types has never been reported. CASE PRESENTATION: A 42-year-old female presented with a palpable mass in diameter of about 2.5 cm in the left breast. Morphologically, the lesion was predominately composed of bland spindle cells admixed with some islands of mature adipocytes and a few epithelial elements dispersing in infiltrating way which formed both tubule and solid structures. The mass showed low positive index of Ki-67. The spindle cells were strongly and diffusely positive for CD34, SMA, desmin, ER and PR. The epithelial elements were positive for CK and EMA, and negative for ER and PR completely. CK5/6 and P63 were positive in the outer-layer of the tubules and nearly all the cells of the solid nests. CONCLUSIONS: A collision tumour of MFB and LGASC in breast is extremely rare and either component is supposed to be not overlooked. Excision and close follow-up are advised.