Background Desmoid-type fibromatosis (DF) is a rare, intermediate, locally aggressive, myofibroblastic neoplasm that develops in musculoaponeurotic tissues. DF has a reported incidence of 2-4 cases per million and accounts for less than 0.03% of all neoplasms; however, despite being benign, rates of local recurrence is high (20-65% at 5 years). DF arise sporadically in most cases (~90%), and whilst most often found in post operative sites of the abdominal wall in women, can arise in any location. DF of the chest wall and breast are exceedingly scarce, with few case reports documenting occurrences post lumpectomy, mastectomy, reduction, and implant-based augmentation. Case report Despite an uncomplicated course 3 years post muscle sparing transverse rectus abdominus myocutaneous (msTRAM) free flap reconstruction for mastectomy, a 61yo female self-detected a new, firm, non-mobile left parasternal lump. We present a case report of DF found intimately adhered to and invading the vascular pedicle of a msTRAM free flap. The patient underwent excision of the DF, which was found to be encasing one of the anastomosed veins. This represents the only documented case report of DF successfully excised from the pedicle of a free flap without flap loss. Conclusion DF is a rare locally aggressive tumour that develops in musculoaponeurotic tissues. Given the abdominal wall in women is a common site of occurrence, the frequency with which these tissues are used in autologous breast reconstruction, and that isolated cases have been found to occur in the post operative breast, surgeons should consider desmoid-type fibromatosis as part of the differential diagnosis when assessing their post reconstructive patients with new breast lumps.