Ultrasonographic findings of invasive micropapillary carcinoma of the breast: correlation between internal echogenicity and histological findings

Invasive micropapillary carcinoma of the breast (IMPC) has been considered to have no specific image finding. The purpose of this study was to correlate the ultrasonographic findings of IMPC, especially internal echogenicity, with histological findings and to discuss the histological factor that influenced the internal echogenicity. Six patients who had undergone surgery at our institute between October 2005 and February 2010 and had been subsequently diagnosed with IMPC were enrolled in this study. Internal echogenicities were correlated with the presence or absence of the central lumens within tumor cell clusters, and with the size of the spaces around these tumor cells. The internal echogenicities of three IMPCs were isoechoic compared with subcutaneous fat tissue, and those of the other three IMPCs were hypoechoic. All three isoechoic IMPCs had central lumens, while no central lumen was seen in the three hypoechoic IMPCs. There was no relation between the size of spaces around the tumor cells and internal echogenicity. All tumors showed either posterior enhancement or no posterior acoustic feature. Half of the IMPCs in our study showed isoechogenicity on ultrasonography. The existence of a central lumen in the tumor cell clusters might have contributed to relatively high internal echogenicity of these IMPCs.