**Acknowledgements**

complex [10, 24]. Therefore MUC1 may play a role in tumor invasion and metastases by disrupting cell adhesions [10]. Similarly, our case of tumor invasion may correlate with the

Additionally, our case of all the tumor cells was positive for MUC3 immunostaining. Rakha et al. and Furuya et al. [26, 27] reported that MUC3 immunostaining is useful for distinguishing between benign lesion and malignant lesion of the breast carcinoma. Our case is concordant with their reports, and membrane-bound mucin of MUC3 may mediate signal transduction correlate with malignancy. Furthermore, Rakha et al. [26] indicated that most breast carcinomas express MUC1, MUC3, and MUC4; however, MUC1 and MUC3 are potential prognostic indicators. Hence, diagnosing invasive lobular carcinoma with extracellular mucin is impor-

Early genomic studies revealed very little overall difference in genomic profiles between low-grade invasive ductal carcinoma and classical invasive lobular carcinoma, implying that classical invasive lobular carcinoma might represent a subtype of low-grade invasive ductal carcinoma [10]. Recent gene expression studies comparing invasive lobular carcinoma and invasive ductal carcinoma have identified two subsets of invasive lobular carcinoma with distinct transcription patterns [10]. Approximately, half of the invasive lobular carcinomas differs from invasive ductal carcinomas in gene expression profiles ("typical" invasive lobular carcinomas), while the remaining invasive lobular carcinomas closely resemble invasive ductal carcinomas in transcription patterns. ("ductal-like" invasive lobular carcinomas) [10]. On the other hand, a recent study on grade- and molecular subtype-matched invasive lobular carcinomas and invasive ductal carcinomas of no special type demonstrated that invasive lobular carcinomas had different transcriptomic profiles in the genes related to cell-to-cell adhesion and signaling, as well as actin cytoskeleton signaling, when compared with gradeand molecular subtype-matched invasive ductal carcinomas [10]. This finding suggested that even though invasive lobular carcinomas and invasive ductal carcinomas might present as a spectrum or form of a family [10]. Taking into consideration of the above Yu et al. reported case, our current case might be in the middle stage of the spectrum between lobular carcinoma and ductal carcinoma. We think existence of extracellular mucin is not definitive for

We encountered the distinct variant of invasive lobular carcinoma with extracellular mucin. We described the correlation of its radiological and pathological interest. Radiological findings of invasive lobular carcinoma with extracellular mucin are documented in English literature for the first time. We suggest one of the MRI special features of our case is not only irregular shaped and margined mass but also small T2-high-signal intensity. These findings by the knowledge from radiopathological correlation might be one of the specific features of invasive lobular carcinoma with extracellular mucin. Further examinations are needed to

MUC1 cytoplasmic expression.

10 New Perspectives in Breast Imaging

tant on not only pathologically but also radiologically.

ductal phenotype not only histologically but also genetically.

**5. Conclusion**

clarify this lesion.

We thank Shigeko Ohnuma and Manabu Kubota department of the St. Marianna University of pathology for their technical assistance and advices.
