Pleomorphic lobular carcinoma in situ (PLCIS) is a relatively uncommon subtype of lobular neoplasia, characterized by large pleomorphic discohesive cells exhibiting marked nuclear atypia, frequent central comedo-necrosis, and microcalcifications. Owing to these features, PLCIS is difficult to distinguish using radiological and histological analyses with high-grade ductal carcinoma in situ. This report presents a case in which breast PLCIS was initially misdiagnosed as invasive ductal carcinoma based on core-needle biopsy and radiological findings. However, further investigation confirmed the diagnosis of PLCIS with invasive lobular carcinoma, measuring only 1.04 mm. This case illustrates the diagnostic challenges of PLCIS, which mimics invasive ductal carcinoma, causing unnecessarily aggressive treatment. Notably, this warrants careful pathological and radiological evaluations for accurate diagnosis and guides appropriate management.