Medullary carcinoma of the breast

Last revised by Joshua Yap on 13 Aug 2022

Medullary carcinoma of the breast (MCB) is an uncommon subtype of breast cancer and accounts for ~5% 1,4 of all breast cancers.

They tend to occur more frequently in younger women than other breast cancer types 7. The mean age of presentation varies from 46-54 years but in 10% of cases, they may present in women under 35 years.

Clinically, these tumors are characterized by rapid growth and therefore often manifest as palpable masses. Lesions can be quite large at presentation.

MCB typically arises from supporting stromal cells of the breast 3. The World Health Organization (WHO) criteria for diagnosis are “a well-circumscribed carcinoma composed of poorly differentiated cells with scant stroma and prominent lymphoid infiltration”. Large pleomorphic nuclei prominent nucleoli and high mitotic activity may be seen. The histologic appearance of medullary carcinoma can mimic that of poorly differentiated intraductal carcinoma not otherwise specified. Areas of associated necrosis may be present. In familial form of breast cancer with BRCA1 gene mutation medullary and mucinous cancers are more common.

There are two types of MCB:

  • typical type: has to meet the following criteria:
    • a) syncytial growth pattern of poorly differentiated tumor cells with a high mitotic rate
    • b) prominent lymphoplasmacytic reaction with a circumscribed microscopic appearance-inflammatory reaction must involve 75% of the periphery and must be present diffusely throughout the substance of the tumor
    • c) no glandular or fatty breast tissue should be found within the invasive portion of the tumor
  • atypical type: resembles the usual classic case; it must have at least 75% syncytial growth but does not have the other two features (circumscription and lymphoplasmacytic infiltration)

Many medullary carcinomas tend to be estrogen and progesterone receptor negative.

Typically seen as a circular/oval type mass lesion with ill-defined or circumscribed margins at mammography. There can be varying degrees of lobulation while calcification is usually not a feature.

The mass can be either homogeneously hyperechoic or hypoechoic with mild heterogeneity 1,2. Enhanced through transmission may be present 2. The level of hypoechogenicity can sometimes be marked 8

May show diffuse enhancement post contrast.

The prognosis tends to be better than for invasive ductal carcinoma (NOS). 5-year survival rates of 89-95% have been reported ref.

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