**1. Introduction**

To discriminate between invasive lobular carcinoma and invasive ductal carcinoma is a big theme for both radiologically and pathologically. The limitation of radiologic imaging in the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

detection and evaluation of invasive lobular carcinoma have been recognized for a long time. Whereas, advances in breast radiologic imaging present opportunities to improve the diagnosis of invasive lobular carcinoma.

On mammography, invasive lobular carcinoma is not likely to form calcifications. However, calcifications may be present in benign proliferative lesions such as sclerosing adenosis [1]. The most common manifestations of invasive lobular carcinoma are asymmetric density, irregular, or spiculated mass on mammography [2–4].

On ultrasonography, 60.5% of invasive lobular carcinomas produced "a heterogeneous low-echoic mass with angular or irregular margins and posterior acoustic shadowing." The remaining tumors had various other sonographic characteristics, including 12% that were "ultrasonographically invisible." The sensitivity of ultrasonography for tumors measuring less than 1 cm was 85.7%. Invasive lobular carcinoma of common type tended to produce "focal shadowing without a discrete mass," whereas tumors with pleomorphic histology were seen as "a shadowing mass." Tumors of the alveolar, solid, and signet-ring variant of invasive lobular carcinoma were most often manifested as a "lobulated, well circumscribed mass" [5]. Ultrasonography is useful and more accurate than mammography in diagnosing invasive lobular carcinoma [5]. However, it is difficult to narrow down the diagnosis of invasive lobular carcinoma.

Breast magnetic resonance imaging (MRI) has an overall sensitivity of 93% for detecting invasive lobular carcinoma, similar to the detection of breast cancers overall (90%). On MRI, tumor of smooth margin, or absence of smooth margin and the distribution of nonmass-like enhancement are the features of invasive lobular carcinoma. Invasive lobular carcinoma may present as ductal, segmental, regional, or diffuse patterns [6]. MR imaging is considered to be a useful tool for detecting invasive lobular carcinoma on radiologically.

Pathologically, the invasive lobular carcinoma includes not only classical type (Foote and Stewart advocated in 1946 [7]) but also variants of solid, alveolar, pleomorphic, tubulolobular, signet-ring, trabecular, and mixed types [8].

We encountered a tumor of invasive carcinoma coexisting with mucinous carcinoma-like lesion. At first, the differential diagnoses of this tumor are (i) mixed mucinous-ductal carcinoma, (ii) mucinous carcinoma with neuroendocrine feature, (iii) mucinous papillary neoplasms, and (iv) carcinoma of mixed type (lobular and ductal carcinoma). Lobular carcinoma has been considered a variant of mucin-secreting carcinoma with only intracytoplasmic mucin [9–11]. In common practice, a diagnosis of mucinous carcinoma or ductal carcinoma with mucinous features is often made in the presence of extracellular mucin, without immunohistochemical confirmation of the ductal phenotype [10]. However, final diagnosis was "invasive lobular carcinoma with extracellular mucin" which has been reported only in three cases in the English medical literature [9–11]. Accordingly, the current report is the fourth documented case in pathology, and in the viewpoint of radiology, this is the first case.

Taking into consideration of the above information, we will discuss the unique variant of "invasive lobular carcinoma with extracellular mucin" with radiopathological correlation.
