Background: Gastrointestinal stromal tumor (GIST) is a mesenchymal tumor of the gastrointestinal tract. Very few cases of coexistence of GIST and adenocarcinoma in other organs have been described.
Case presentation: We present the case of a 63-year-old female patient diagnosed with breast cancer. After five years of the diagnosis, the findings of colon adenocarcinoma and GIST in stage IA were discovered incidentally during surgical treatment of the colon carcinoma. This tumor display: mixed spindle-epithelioid cell cytological type, of moderate cellularity, mitotic index (1∕10) with low anaplasia, low proliferative status (Ki-67 index 12%), without necrosis and immunophenotype profile: antiendomysial antibody (EMA)-, vimentin+++, CD117++, CD34+++, alpha-smooth muscle actin (α-SMA)+, desmin+∕-, S-100-, CD68-.
Conclusions: The present case is extremely rare since the patient has adenocarcinoma with GIST in a previously diagnosed breast carcinoma. Based on this, in clinical practice should always think about possibility occurrence of synchronous and metachronous tumors.