General

• IDC is the most common type of invasive breast CA (70-80%)

• Characterized by nests and cords of tumor cells w/ variable amount of gland formation.

• Malignant cells induce a fibrous response as they infiltrate parenchyma leading to characteristic spiculations.

Grades

• Grades are based on architectural and cytologic features

• Well-differentiated / grade 1

  • Tumor cells infiltrate the stroma as solid nests of glands

  • Nuceli are relatively uniform w/ little or no mitotic activity

• Moderately differentiated / grade 2

  • Cells infiltrate as solid nests w/ some glandular differentiation

  • Some nuclear pleomorphism is present w/ moderate mitotic rate

• Poorly-differentiated / grade 3

  • Composedof solid nests of cells w/o gland formation

  • Marked nuclear atypia and considerable mitotic activity

General

• ILC is the 2nd MC type of invasive breast CA (5-10%)

  • ILC has a higher frequency of bilateral and multicentric dz

  • ILC is seen in older women and are larger and better differentiated

  • ILC is ER positive as a rule

  • Outcomes are more favorable w/ ILC

  • ILC tends to mets later than IDC

    • ILC spreads to unusual sites such as peritoneum, meninges, and GIT

    • IDC spreads to bone, liver, lung, and brain

• Incidence is increasing faster than rates of IDC; more strongly associated w/ HRT

• Macroscopic appearance is identical to IDC; microscopic extent may be greater than macroscopic

  • Microscopically characterized by small cells that infiltrate stroma and adipose tissue individually in a single file pattern -> induces only a minimal fibrous reaction as opposed to IDC

• Pathologists use the lack of E-cadherin staining to distinguish ILC from IDC

• In many cases, no mass lesion is evident

  • ILC is more likely to be an asymmetry than a mass forming lesion.

• Due to this and propensity of bilateral and multicentric dz, bx proven cases are recommended to have MRI

• Accounts for 1-2% of invasive breast CA

• More common in older patients

• Tends to be well-circumscribed

• Nest of tumor cells dispersed in large pools of extracellular mucus; uniform cells w/ low grade nuclei

• Favorable prognosis

• Accounts for 1-10% of invasive breast CA

• Well circumscribed macroscopically

• Tumors cells are poorly differentiated (high-grade), grow in a syncytial pattern, and have intense lymphoplasmacytic infiltrate

• Seen in younger patients

  • Most frequent in those w/ BRCA1 gene (10% compared to <1% general pop)

• Prognosis of pure medullary carcinoma is somewhat more favorable than IDC