Mucinous carcinoma of the breast

Mucinous carcinoma of the breast is a sub-type of invasive ductal carcinoma (IDC). They account for about ~ 2% (range 1 - 7 % ⁴) of breast cancers. 

Epidemiology

It tends to occur in older women where a prevalence of as much as 7% is found among women 75 years or older, whereas the prevalence is only 1% in women younger than 35 years ⁴. 3/4 5 year survival

Clinical presentation

If palpable, they tend to manifest as soft masses.

Pathology

It  is formed by mucus-producing cancer cells and contains large amounts of extracellular epithial mucin surrounding and within tumour cells. The growth pattern is often expanding, cellularity and mitotic activity are low, and cell atypia is not very prominent.

At pathological examination, the dominant feature is the presence of mucin. The mucin to cell ratio can vary from lesion to lesion. A core biopsy specimen usually gives a gelatinous appearance.

It can histologically divided into two broad types

• pure mucinous breast cancer - entire tumour consists of cells with excessive extracellular mucin surrounding them
• mixed mucinous breast cancer - tumour also contains areas with infiltrating ductal carcinoma devoid of extracellular mucin.

Radiographic features

Because of different patterns mammographic and ultrasound, both should be performed in all cases of MCB.

Mammography

The presence of mucin results in a low-density and relatively well-defined lobular mass. Sometimes they may have partly faded or obscure margins. Up to 20% of lesions can be occult on mammography ⁴. Calcification can be rare in pure mucinous types.

Ultrasound

At ultrasound, mucinous carcinomas often display mixed echogenicity with mixed solid and cystic components. Posterior acoustic enhancement is common. As times the lesion can be iso-echoic to breast tissue on ultrasound which can in make diagnosis difficult ³.

Sonographically, mixed cystic and solid components, distal enhancement, and microlobulated margins are commonly found in mucinous carcinomas. Homogeneity on sonography is associated with the pure type of MCB, in which margins are usually well defined, and the tumour is iso-echogenic relative to the fat surrounding the breast tissue on ultrasound. A mixed MCB tends to be more hypo-echoic.

Breast MRI

On MRI, they are one of the few cancers that have very high signal intensity on T2-weighted images ² which relates to the water component in mucin. Post contrast enhancement as times can be very low or minimal.

Prognosis

A pure mucinous sub type carries a better prognosis. Overall tendency to metastasize is less than for other commoner types of cancer (e.g. invasive ductal carcinoma not otherwise specified (NOS). Mixed MCB have a more aggressive behaviour

See also

• breast neoplasms