Are Mucinous Carcinomas of the Breast Hard on Elastography?

Mucinous carcinomas are a rare type of invasive breast carcinoma characterized by large quantities of extracellular mucin on histopathological examination. These tumors can be easily missed or misdiagnosed. Due to large quantities of mucin, these tumors are presumed to be "soft" masses. This pilot study aims to evaluate the strain and shear wave elastography features of these tumors. Out of 485 referred patients with breast cancer between November 2022 and January 2023, 8 cases were diagnosed as mucinous carcinoma breast on histopathology. These were evaluated with strain and shear wave ultrasound elastography in addition to mammography and B-mode ultrasound. Tsukuba elasticity score, fat-to-lesion ratio (FLR), and distance ratios were calculated on strain elastography. Mean elasticity values as well as elasticity ratio were evaluated on shear wave elastography. On mammography, 3/8 masses were equal density, 2/8 were low density, 2/8 were high density, and 1/8 showed extensive calcifications. Microlobulated margins were seen in 6/8 masses, and the rest (2/8) showed circumscribed margins. On ultrasound, 4 masses appeared isoechoic, and the remaining 4 were hypoechoic. On strain elastography, 7/8 (87.5%) masses had Tsukuba elasticity scores of 4 and above; 6/8 had FLR >4.8 and 6/8 had distance ratios >1. The mean elasticity value on shear wave was 149.12 kPa, and the shear wave elasticity ratio was 8.9. Interestingly, despite the presence of large quantities of extracellular mucin in these tumors, mucinous tumors have elastography findings similar to solid malignant breast masses. Hence, elastography is a useful tool in detecting these often-benign-looking masses.