Test ID: ICOSI    
ICOS (CD278), Immunostain, Technical Component Only

Useful For Suggests clinical disorders or settings where the test may be helpful

Classification of T-cell lymphomas

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

For the initial technical component only immunohistochemical (IHC) stain performed, the appropriate bill-only test ID will be reflexed and charged (IHTOI). For each additional technical component only IHC stain performed, an additional bill-only test ID will be reflexed and charged (IHTOA).

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

ICOS (inducible T-cell costimulator or CD278: cluster of differentiation 278) is primarily expressed on activated CD4+ and CD8+ T cells where it regulates immune responses and plays a role in the regulation of T-follicular helper cells. ICOS is a sensitive marker for identifying T-cell lymphomas of follicular helper T-cell origin, especially certain patterns of angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphomas with T-follicular helper phenotype (PTCL-TFH).

Interpretation Provides information to assist in interpretation of the test results

This test does not include pathologist interpretation, only technical performance of the stain. If interpretation is required order PATHC / Pathology Consultation for a full diagnostic evaluation or second opinion of the case.


The positive and negative controls are verified as showing appropriate immunoreactivity. If a control tissue is not included on the slide, a scanned image of the relevant quality control tissue is available upon request. Contact 855-516-8404.


Interpretation of this test should be performed in the context of the patient's clinical history and other diagnostic tests by a qualified pathologist.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Age of a cut paraffin section can affect immunoreactivity. Stability thresholds vary widely among published literature and are antigen dependent. Best practice is for paraffin sections to be cut within 6 weeks.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Baseggio L, Traverse-Glehen A, Berger F, et al: CD10 and ICOS expression by multiparametric flow cytometry in angioimmunoblastic T-cell lymphoma. Modern Pathology. 2011 Jul;24(7):993-1003

2. Tan LH, Tan SY: Aberrant immunoarchitecture distinguishes hyperplastic germinal centres in pattern 1 angioimmunoblastic T-cell lymphoma from reactive follicles. Hematol Oncol. 2014;32(3):145-154

3. Bosisio FM, Cerroni L: Expression of T-follicular helper markers in sequential biopsies of progressive mycosis fungoides and other primary cutaneous T-cell lymphomas. Am J Dermatopathol. 2015;37(2):115-121