Immunostains

Question 1

CD31

Answer 1

Stains:
Endothelial cells and megakaryocytes
(cytoplasmic and membranous), also
macrophages.

Used:
To identify endothelial differentiation or angiosarcoma;
most specific endothelial marker.

Question 2

CD34

Answer 2

Stains:
Endothelial cells, fibroblasts, and
hematopoietic blasts (cytoplasmic
and membranous).

Used:
To identify vascular sarcomas, Kaposi sarcoma, solitary
fibrous tumor, DFSP (dermatofibrosarcoma protuberans), epithelioid sarcoma, plus some other soft tissue tumors. Synovial sarcoma is negative

Question 3

D240

Answer 3

**Stains:**
Lymphatic endothelium (cytoplasmic).

Used:
To identify vascular differentiation or lymphatics; also
marks mesothelium

Question 4

FVIII

Answer 4

Stains:
Endothelial cells, megakaryocytes,
platelets (cytoplasmic).

Used:
To identify endothelial differentiation, specific but not
very sensitive

Question 5

CK903 (CK5/6 is similar)

Answer 5

Stains:
Myoepithelial cells (cytoplasmic and membranous) and usual duct hyperplasia; High-molecular-weight keratins, mainly
in squamous and urothelial epithelia (cytoplasmic and membranous)

Used:
To differentiate usual ductal hyperplasia (positive) from ductal carcinoma in situ (negative). Also stains metaplastic carcinoma. To identify prostatic basal cells (loss of staining
indicates carcinoma) and urothelial carcinoma (positive); also metaplastic breast carcinoma

Question 6

E-cadherin

Answer 6

Stains:
Normal ductal and lobular cells (membranous)

Used:
Loss of staining identifies lobular carcinoma (in situ and invasive); ductal lesions are positive

Question 7

ER and PR

Answer 7

**Stains:**
Estrogen receptor (nuclear) and progesterone receptor (nuclear)

Used:
For breast cancer prognosis (predicts response to tamoxifen) and to identify metastatic breast cancer, some gynecologic tumors, and others

Question 8

GATA3

Answer 8

**Stains:**
Breast epithelium (nuclear

Used:
To identify breast differentiation in carcinoma; sensitive but not specific

Question 9

GCDFP

Answer 9

Stains:
Apocrine metaplasia of the breast and apocrine sweat glands (cytoplasmic)

Used:
To identify breast differentiation in carcinoma, also sweat and salivary gland carcinoma

Question 10

Her2

Answer 10

Stains:
Growth factor receptor that is only weakly expressed in normal epithelial cells (membranous)

Used:
To evaluate breast carcinomas (overexpression is a poor prognostic sign but can be treated with Herceptin)

Question 11

Mammoglobin

Answer 11

Stains:
Normal breast tissue (cytoplasmic)

Used:
To identify breast differentiation in carcinoma, also sweat and salivary gland carcinoma

Question 12

Calponin

Answer 12

**Stains:**
Myoepithelial cells (cytoplasmic)

Used:
To delineate myoepithelial layer to identify myoepithelial cells to rule out invasive carcinoma

Question 13

p63

Answer 13

Stains:
Tumor suppressor gene (nuclear)

Used:
To identify myoepithelial cells to rule out invasive carcinoma.Stains myoepithelial cells but not endothelium and fibroblasts. Also stains metaplastic carcinoma.

Question 14

Smooth muscle myosin heavy chain (SMMHC)

Answer 14

Stains:
Myoepithelial cells, blood vessels, myofibroblasts (cytoplasmic)

Used:
To identify myoepithelial cells to rule out invasive carcinoma. To delineate myoepithelial layer

Question 15

Smooth muscle actin (SMA)

Answer 15

Stains:
Smooth muscle: myoepithelial cells, blood vessels, myofibroblasts (cytoplasmic)

Used:
To identify myoepithelial cells to rule out invasive carcinoma. To delineate myoepithelial layer; also stains myofibroblasts

Question 16

Calcitonin

Answer 16

Stains:
C cells of the thyroid (cytoplasm and extracellular material)

Used:
To identify medullary carcinoma of the thyroid

Question 17

PAX8

Answer 17

Stains:
Renal and Mullerian tissues (nuclear)

Used:
To identify anaplastic carcinoma of thyroid and other
thyroid carcinomas

Question 18

Thyroglobulin

Answer 18

**Stains:**
Thyroid follicles (cytoplasmic)

Used:
To identify metastatic thyroid carcinoma

Question 19

TTF-1 (thyroid transcription factor)

Answer 19

Stains:
Transcription factor in the lung and thyroid (nuclear)

Used:
To identify thyroid carcinoma, including follicular,
papillary, and medullary; also nonsquamous carcinoma
of the lung (adenocarcinoma and small cell)

Question 20

AE1-AE3 (pankeratin)

Answer 20

Stains:
Wide panel of keratins stains most epithelial cells (cytoplasmic), except cytokeratins 8 and 18

Used:
To identify carcinomas in general; used in conjunction with cam 5.2 to screen for carcinoma

Question 21

EMA

Answer 21

Stains:
Epithelial, perineural, meningothelial cells (cytoplasmic or membranous)

Used:
To identify meningioma, many carcinomas, plus some sarcomas (synovial sarcoma, epithelioid sarcoma), and plasma cell neoplasms. Germ cell tumors (excluding some teratomas) are negative

Entities that are EMA-positive, keratin-negative: meningioma, perineuroma, plasma cell myeloma

Question 22

CK5/6

Answer 22

Stains:
High-molecular-weight keratins, mainly in squamous and urothelial epithelia (cytoplasmic)

Used:
To differentiate squamous cell carcinoma (positive) or mesothelioma (positive) from adenocarcinoma
(negative)

Question 23

CK7

Answer 23

Stains:
A specific low-molecular-weight cytokeratin (cytoplasmic, membranous)

Used:
CK7 and CK20 are used in combination to narrow the differential of carcinoma of unknown origin. CK7 is generally positive in above-the-diaphragm carcinomas (see below on CK7 and CK20)

Question 24

CK20

Answer 24

Stains:
A specific low-molecular-weight cytokeratin (cytoplasmic, membranous)

Used:
Generally positive in below-the-diaphragm carcinomas and in Merkel cell carcinoma (see below on CK7 and CK20)

Question 25

Cam 5.2

Answer 25

Stains:
Low- and intermediate-molecular-weight keratins 8, 18, and 19, in nonsquamous epithelia (cytoplasmic)

Used:
Used in conjunction with AE1/AE3 to screen for carcinoma. Also to identify hepatocellular carcinoma, some adrenal cortical tumors, and some carcinomas that are negative for other keratins (undifferentiated carcinoma)

Question 26

CK 7/20 Matrix

7+20+; 7+20-

7-20+; 7-20-

Answer 26

7+20+: urothelial carcinoma, pancreatic carcinoma, ovarian mucinous carcinoma

7+20-: breast carcinoma, lung carcinoma (non-small cell), ovarious serious carcinoma, endometrial carcionma, epithelial mesothelioma, thymoma

7-20+: Colorectal carcinoma, merkel cell carcinoma

7-20-: Hepatocellular carcinoma, renal cell carcinoma (clear cell type), prostate carcinoma, neuroendocrine small cell carcinoma, squamous cell carcinoma