The management of papillary lesions of the breast diagnosed on core needle biopsy is highly contentious. Papillary lesions are epithelial proliferations of breast tissue and are on a continuum of mutations with atypical hyperplastic lesions and in situ carcinoma. With the current literature suggesting that excisional biopsy of papillary lesions might not be required, we discuss a unique case that suggests otherwise. We present a 21-year-old woman with multiple papillary lesions on core biopsy of a breast lesion, and a subsequent excisional biopsy revealing extensive in situ carcinoma of the breast. This finding necessitated total mastectomy. This unique case highlights that core biopsy specimens are unable to effectively exclude adjacent in situ carcinoma and suggests that papillary lesions diagnosed on core needle biopsy require excisional biopsy.