Neuroendocrine differentiation in breast cancer recognized since 1963 but hindered by frequently changing terminology and diagnostic criteria. Breast Carcinoma of No Special Type with neuroendocrine differentiation (IBC-NST-NE) is diagnosed by identifying the presence and extent of NE features. This case report emphasize the significance of establishing IBC-NST-NE diagnose. A 75-year-old woman presented with a year-old left breast lump, rapidly enlarging over 3 months with multiple ulceration and bloody nipple discharge. Needle biopsy confirmed ductal carcinoma. Radical mastectomy revealed a 7,5x7,3x4,9 cm, gray-white, lobulated mass with indistinct borders. Histopathology identified invasive ductal carcinoma with 30% exhibiting NE features—arranged in insular and pseudorosette pattern, composed of polygonal cells with granular cytoplasm and salt-and-pepper chromatin. Synaptophysin and chromogranin A were positive in neuroendocrine component leading to the IBC-NST-NE diagnosis. Therapy of IBC-NST-NE follow standard IBC protocol, however it have shorter disease-free survival , poorer survival rate, higher distant metastasis rates and higher TNM stage at diagnosis. Diagnosing IBC-NST-NE is crucial for prognosis and enhance our understanding of neuroendocrine differentiation behaviour in breast cancer.