Primary small cell carcinoma (SCC) of the breast, an exceedingly rare and aggressive tumor, is often characterized by rapid progression and poor prognosis. We report a case of primary SCC of the breast that was diagnosed through pathologic and immunohistochemical examinations. Computed tomography (CT) scans failed to reveal a non-mammary primary site. Due to the scant number of relevant case summaries, this type of tumor is proved to be a diagnostic and therapeutic challenge. Therefore, we also reviewed relevant literature to share expertise in diagnosis, clinicopathologic characteristics, treatment, and prognosis of this type of tumor. Future studies with more cases are required to define more appropriate treatment indications for this disease. Primary small cell carcinoma (SCC) of the breast, an exceedingly rare and aggressive tumor, is often characterized rapid progression and poor prognosis. We report a case of primary SCC of the breast that was diagnosed through pathologic and immunohistochemical examinations. Computed tomography ( CT) scans failed to reveal a non-mammary primary site. Due to the scant number of relevant case summaries, this type of tumor is proved to be a diagnostic and therapeutic challenge. Therefore, we also reviewed relevant literature to share expertise in diagnosis, clinicopathologic characteristics, treatment, and prognosis of this type of tumor. Future studies with more cases are required to define more appropriate treatment indications for this disease.