ALK (Anaplastic Lymphoma Kinase) is a transmembrane molecule that is only normally expressed in some neural tissues. It has characteristic expression in a significant proportion of Anaplastic Large Cell Lymphoma (ALCL) cases. It has also been expressed in cases of pleomorphic liposarcoma, inflammatory myofibroblastic tumor and a small subset of diffuse large B-cell lymphomas.
A subset (1-5%) of non-small cell lung carcinomas (usually adenocarcinomas) have an ELM4-ALK mutation, which is often sensitive to the tyrosine kinase inhibitor (TKI) crizotinib (Pfizer). Newer TKIs, including ceritinib (Novartis) and alectinib (Hoffmann-La Roche), have also been found to be effective.
Historically, ALK translocations have been identified by FISH analysis. IHC is also an accepted method with an FDA approved test (IHC CDx Assay). PCR is being studied as an alternative. ALK antibody clones 5A4 (Novocastra, Leica Biosystems, Buffalo Grove, Illinois), ALK1 (Dako, Santa Clara, California), 1A4 (Origene, Rockville, Maryland) and D5F3 (Cell signaling Technology, Danvers, Massachusetts) have been successfully used to identify ALK mutated lung tumors, with the 5A4 & D5F3 having equivalent sensitivity. The ALK1 clone is not as sensitive and the 1A4 clone lacks specificity compared to other antibodies. Please consult the current medical literature for FDA approved tests for ALK translocation identification in non-small cell lung carcinomas.
- Neural Tissue
- Anaplastic Large Cell Lymphoma
- Pleomorphic Liposarcoma
- Subset of Diffuse Large B-Cell Lymphoma
- Inflammatory Myofibroblastic Tumors
- Merkel Cell Carcinoma (KIF5B-ALKrearrangement)
ALK may stain in a cytoplasmic and/or nuclear pattern. In ALCL the combined pattern of cytoplasmic and nuclear staining is associated with the t(2;5).
In lung ALK staining/expression is cytoplasmic. Like other markers (e.g. Napsin A), staining may be present in macrophages. Necrotic tumor, extracellular mucin, and cells of neural origin may also stain.
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Yi, E. S., Boland, J. M., Maleszewski, J. J., Roden, A. C., Oliveira, A. M., Aubry, M.-C., et al. (2011). Correlation of IHC and FISH for ALK Gene Rearrangement in Non-small Cell Lung Carcinoma: IHC Score Algorithm for FISH. Journal of Thoracic Oncology : Official Publication of the International Association for the Study of Lung Cancer, 6(3), 459–465. doi:10.1097/JTO.0b013e318209edb9
Mino-Kenudson, M., Chirieac, L. R., Law, K., Hornick, J. L., Lindeman, N., Mark, E. J., et al. (2010). A novel, highly sensitive antibody allows for the routine detection of ALK-rearranged lung adenocarcinomas by standard immunohistochemistry. Clinical Cancer Research : an Official Journal of the American Association for Cancer Research, 16(5), 1561–1571. doi:10.1158/1078-0432.CCR-09-2845
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CK5 is a high molecular weight cytokeratin that stains stratified squamous epithelium (e.g. skin, tongue mucosa, etc.), basal cells of the prostate gland, myoepithelial cells in breast tissue, and mesothelial cells/mesothelioma. Therefore CK5 is a versatile marker, which can be used in a variety of diagnostic applications.
CK5 is useful in the diagnosis of squamous cell carcinoma, urothelial carcinoma, mesothelioma, thymic tumors, and skin appendage tumors. It is also helpful in identifying the myoepithelial layer in breast tissue, and the basal layer in prostate tissue. The combined expression of p63 and CK5 in poorly differentiated tumors is highly suggestive of squamous origin (Kaufmann, O., et al).
CK5 will stain approximately 70-80% of squamous cell carcinomas with a cytoplasmic staining pattern. p63 is considered slightly more sensitive, but may give varying positivity in cases of lung adenocarcinoma that can be confusing. Therefore, CK5 and p63 are often used as part of a panel to diagnose squamous cell carcinoma. Since p63 is a nuclear marker, these two stains can be performed as a double stain on a single slide with one or two different chromogens.
CK5 is an excellent marker for the basal layer, and stains in a similar pattern to 34betaE12. Again, CK5 can be combined with p63, which also stains the basal layer of prostate glands.
Urothelial carcinoma will typically express p63 diffusely with variable reports of CK5 or CK5/6 expression in urothelial carcinoma.
CK5 will stain the myoepithelial layer of breast tissue, but other markers such as smooth muscle myosin and calponin are typically used more commonly. Basal-like breast carcinomas usually express CK5, especially with the monoclonal CK5 antibody compared to CK5/6 (Bhargava, R, et al). Metaplastic/sarcomatoid breast carcinomas have also been reported to express CK5.
CK5 will stain the stratified squamous epithelium. If there are cells in the squamous epithelium, which may be Paget cells or melanocytes, CK5 can be used along with CK7 or Melan A/HMB-45 to differentiate between odd appearing keratinocytes, Paget's disease, or melanocytes.
CK5 vs. CK5/6
There is still occasionally discussion as to which is a better marker. Some feel CK5/6 is a better marker since it has more than one cytokeratin in its cocktail. However, there is a very strong consensus among pathologists who have used both that CK5 performs significantly better than CK5/6, and is therefore, the preferred antibody.
Common expression patterns in carcinoma (Chu, PG, et al).
|Skin: BCC & SCC||100%||Squamous|
|Squamous Salivary Gland Tumors||100%||Myoepithelial|
|Ovarian Ca. (Serous)||75%||Serous Epithelium|
Note: other references note a much higher + expression pattern in mesotheliomas This may be dependent upon the mix of epithelial and sarcomatous variants.
CK5 is a high molecular weight cytokeratin expression by stratified epithelium (epidermis) and myoepithelial/basal layer cells.
p63/CK5 (double stain) with p63 nuclear expression (DAB) and CK5 cytoplasmic expression (red)
Lung squamous cell carcinoma with p63 nuclear expression (DAB) and cytoplasmic CK5 expression (red).
CK5/6 expression in a lung squamous cell carcinoma. CK5/6 tends to have more varied expression compared to the monoclonal CK5 antibody.
Fichtenbaum EJ, Marsh WL, Zynger DL. CK5, CK5/6, and double-stains CK7/CK5 and p53/CK5 discriminate in situ vs invasive urothelial cancer in the prostate. Am J ClinPathol. 2012;138: 190–197. doi:10.1309/AJCP5ZC4GQVNWTYR
Bhargava, R., Beriwal, S., Mcmanus, K., & Dabbs, D. J. (2008). CK5 is more sensitive than CK5/6 in identifying the “basal-like” phenotype of breast carcinoma. American Journal of Clinical Pathology, 130(5), 724–730. doi:10.1309/AJCP3KFF1LTYWQIY
Mukhopadhyay, S., &Katzenstein, A.-L. A. (2011). Subclassification of non-small cell lung carcinomas lacking morphologic differentiation on biopsy specimens: Utility of an immunohistochemical panel containing TTF-1, napsin A, p63, and CK5/6. The American Journal of Surgical Pathology, 35(1), 15–25. doi:10.1097/PAS.0b013e3182036d05
Kaufmann, O., Fietze, E., Mengs, J., &Dietel, M. (2001). Value of p63 and cytokeratin 5/6 as immunohistochemical markers for the differential diagnosis of poorly differentiated and undifferentiated carcinomas. American Journal of Clinical Pathology, 116(6), 823–830. doi:10.1309/21TW-2NDG-JRK4-PFJX
Chu, P. G., & Weiss, L. M. (2002). Expression of cytokeratin 5/6 in epithelial neoplasms: an immunohistochemical study of 509 cases. Modern Pathology : an Official Journal of the United States and Canadian Academy of Pathology, Inc, 15(1), 6–10. doi:10.1038/modpathol.3880483