Invasive breast carcinoma of no special type

Invasive breast carcinoma of no special type, previously known as invasive ductal carcinoma, not otherwise specified, is the most common type of breast cancer (70-80%) ⁵. It is an infiltrating and malignant proliferation of neoplastic cells in the breast tissues.

Terminology

The 4^th edition (2012) of the WHO classification of tumors of the breast changed the preferred terminology from "invasive ductal carcinoma (IDC), not otherwise specified (NOS)" to "invasive breast carcinoma (IBC) of no special type (NST)" ⁴. The rationale is that the term "ductal" relies on unproven histogenetic assumptions for this heterogeneous group of cancers. "Invasive ductal carcinoma" or "ductal NOS" remain acceptable and commonly used terms. 

Epidemiology 

The peak age of presentation is about 50-60 years. The Black population has a higher predisposition to grade 3 cancer and also a higher mortality rate.

Clinical presentation 

Often presents as a large palpable, immobile mass.

Pathology

Grading

The Nottingham combined histologic grade system, also called the modified Scarff-Bloom-Richardson grading system, is recommended by the College of American Pathologists. This grading system is based on the following criteria ⁶: 

• tubule formation

  • 1 point: >75% of the tumor (majority of tumor)

  • 2 points: 10-75% of tubular formation

  • 3 points: <10% of tubular formation

• nuclear pleomorphism

  • 1 point: nuclei with minimal or mild variation in size and shape

  • 2 points: nuclei with moderate variation in size and shape

  • 3 points: marked variation in size and shape

• mitotic activity

  • 1 point: 0-5 per 10 high power fields (HPFs)

  • 2 points: 5-10 per 10 HPFs

  • 3 points: >10 per 10 HPFs

• overall score

  • 3-5 points: grade 1 or well-differentiated tumor

  • 6-7 points: grade 2 or moderately-differentiated tumor

  • 8-9 points: grade 3 or poorly-differentiated tumor

Radiographic features

Mammography

• irregular mass with or without calcifications

• spiculated and hyperdense: 41% in grade 1 and 26% in grade 3

• circumscribed: more commonly grade 3 (36%) 

• microcalcifications: 34% in grade 1 and 37% in grade 3 ⁵

  • amorphous: associated with low grade

  • pleomorphic: associated with high grade

Ultrasound

• ill-defined

• hypoechoic mass

• hyperechoic angular margins

• posterior acoustic shadowing: 71% in grade 1

• posterior enhancement: 45% in grade 3

• ductal extension may be seen: represents extension of the mass into the surrounding parenchyma

• branched or spiculated pattern

• microcalcifications

Elastography

Elastography depicts increased stiffness of the mass and the surrounding tissue. This feature correlates with the tumor grade ⁵.

MRI

• T1

  • isointense to breast parenchyma

  • hypointense to fat

• T1 C+ (Gd)

  • irregular or spiculated mass

  • ring enhancement with centripetal progression, or non-mass enhancement (NME)

  • dilated veins draining the tumor

  • kinetic curves

    • early wash-in: higher initial enhancement ratio (IER)

    • wash-out or plateau kinetic curves (76-91%)

• T2

  • iso to hypointense to parenchyma

  • hyperintense edematous zone

Treatment and prognosis

The Nottingham prognostic index (NPI) is used to determine the prognosis for invasive breast carcinoma after surgery ⁷.

NPI = (0.2 x S) + N + G

• S: size of the lesion in centimeters

• N: node status

  • 0 nodes = 1

  • 1-3 nodes = 2

  • >3 nodes = 3

• G: grade of tumor (1 to 3)

Interpretation:

• NPI ≤2.4 = excellent: 96% cancer-specific 10-year survival

• NPI >2.4 and ≤3.4 = good: 93% cancer-specific 10-year survival

• NPI >3.4 and ≤5.4 = moderate: 78% cancer-specific 10-year survival

• NPI >5.4 = poor: 44% cancer-specific 10-year survival