https://doi.org/10.1177/0300891619870247 Tumori Journal 1–4 © Fondazione IRCCS Istituto Nazionale dei Tumori 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0300891619870247 journals.sagepub.com/home/tmj TJ Tumori Journal Introduction Sclerosing adenosis (SA) is a benign lesion originating from the terminal ductal lobular unit of the breast and characterized by glandular and stromal proliferation, 1 first described by McDivitt et al. in 1968. 2 It is classified under benign epithelial proliferations by the World Health Organization. 3 Although clinically and pathologically SA has benign behavior, it can mimic carcinoma in situ (CIS) and invasive carcinoma radiologically, grossly, and histologically. 4 The etiology of SA is not clear but it is believed to be a lesion developing in response to an abnormal hormonal environment. Like the other benign proliferative lesions without atypia, SA results in a 1.7 to 3.7 fold increased risk of breast cancer throughout life. 5 SA may be associated with other benign proliferative lesions such as intraductal papilloma and fibroadenoma, and may also accompany proliferative lesions with atypia A case of extensive ductal carcinoma in situ and sclerosing adenosis with metastasis on sentinel lymph node Selin Narter 1 , Secil Hasdemir 1 , Sahsine Tolunay 1 and Sehsuvar Gokgoz 2 Abstract Introduction: Sclerosing adenosis is a form of adenosis characterized by lobulocentric architecture, glandular and stromal proliferation in which the stromal component compresses and distorts the glandular structures. Atypical epithelial proliferations such as atypical lobular hyperplasia, lobular carcinoma in situ, and ductal carcinoma in situ may accompany areas of sclerosing adenosis. We present a case of ductal carcinoma in situ and sclerosing adenosis with metastatic carcinoma on sentinel lymph node. Case description: A 40-year-old woman presented with a palpable mass in her left breast. Radiologic studies showed a lesion suggesting malignancy in the left breast and atypical lymph node in the left axillary region. Left lumpectomy and sentinel lymph node biopsy was performed. Histopathologic examination revealed lobulocentric lesions with glandular proliferation and hyalinizing stroma in between. Foci of high-grade cribriform and solid type ductal carcinoma in situ were observed. Sentinel lymph node biopsy showed micrometastasis in one lymph node section. Based on these findings, the patient was diagnosed with high-grade ductal carcinoma in situ with sclerosing adenosis. However, the presence of micrometastasis in the lymph node suggested occult invasion that we were not able to detect. Conclusion: Ductal carcinoma in situ with sclerosing adenosis can mimic invasive carcinoma both radiologically and histologically. It should be kept in mind that there may be occult invasive carcinoma in patients with ductal carcinoma in situ whether the lesion is accompanied by sclerosing adenosis or not. Multiple sections and immunohistochemical studies can be of help. Keywords Breast, Ductal carcinoma in situ, Invasion, Micrometastasis, Sclerosing adenosis Date received: 06 May 2019; accepted: 23 July 2019 1 Department of Surgical Pathology, Faculty of Medicine, Uludag University, Bursa, Turkey 2 Department of General Surgery, Faculty of Medicine, Uludag University, Bursa, Turkey Corresponding author: Selin Narter, Department of Surgical Pathology, Uludag University, Faculty of Medicine, Gorukle, Bursa 16059, Turkey. Email: seelin.narter@gmail.com 870247TMJ 0 0 10.1177/0300891619870247Tumori JournalNarter et al. case-report 2019 Case Report