20% of breast carcinomas are of special type and the majority of these are lobular carcinomas. Tubular and mucinous carcinomas occur next most frequently and thereafter the remaining special types are seen infrequently. In order to make a diagnosis of a special type of carcinoma >90% of the tumour is required to show the particular pattern in question. Special types of carcinoma should be distinguished from mixed carcinomas where the special type areas occupy between 50 and 90% of the tumour area with the remaining area being usually of no special type.
See also Common Cancers

It is recommended that special types of carcinoma are graded using the same criteria as no specicial type cancers.

See also Grading Breast Cancer

See also Prognosis

Invasive carcinomas of special type:

Invasive lobular carcinoma

These tumours, in their classical form, are characterised by a single file infiltrating pattern. Tumour cells are normally intermediate in size and a common finding is the presence of a squared off clear space between adjacent tumour cells. Cytoplasmic vacuolation is common and another frequently encountered feature is the presence of a rather granular eosinophilic cytoplasm. A number of variant forms are recognised (see link below).

classical invasive lobular carcinoma
Classical pattern ILC. Single file runs of tumour cells with squared-off edges. Note apparent clear space at cell-cell interface.

This view emphasises the rigid structures seen in DCIS with apparently cleanly punched out holes
Beta catenin staining of tumour cells (cytoplasmic) and normal duct (membranous) in classical pattern ILC; 'Mouse–over' for aberrant weak staining pattern in corresponding E cadherin preparation but normal strong membrane staining in the normal duct.

Invasive Tubular Carcinoma

Clinical basics:

Histological diagnosis:

Tubular carcinoma
Excision biopsy of tubular carcinoma. Note > 90% tubule formation. 'Mouse‑over' for high power view.

Tubular carcinoma
Tubular carcinoma. 'Mouse‑over' for further view (arrows point to calcs).

tubular carcinoma tubular carcinoma
Low power view of invasive tubular carcinoma (left) and high power view showing single layer of infiltrating tumour cells with striking luminal cytoplasmic apical snouts

Invasive mucinous carcinoma

mucinous carcinoma mucinous carcinoma
Mucinous carcinoma of breast

See also Mucocele-like lesion

Invasive Cribriform Carcinoma

cribriform carcinoma
Cribriform carcinoma of breast

cribriform carcinoma
Cribriform carcinoma. 'Mouse‑over' for further view (arrow points to calcs).

Invasive Medullary-like Carcinoma

medullary-like carcinoma medullary-like carcinoma
medullary-like carcinoma medullary-like carcinoma
Medullary-like Carcinoma - The tumour is very uncommon. It has a pushing margin, a heavy lymphocytic infiltrate, grade 3 features and 'syncitial' morphology (cell boundaries difficult to distinuish). They commonly display a basal phenotype - note positive CK5/6 immunostain.

Medullary carcinoma
Medullary carcinoma - note 'pushing' interface with adjacent breast. 'Mouse‑over' for high power view with grade 3 features and syncitial cytology.

Other Invasive Carcinomas

These include:

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