Diagnostic Tests in Cancer

Immunohistochemistry (IHC)

The American Society of Clinical Oncology recommends IHC as a primary screening tool for cancer diagnosis, classification, and treatment selection, detecting specific protein expression in tissue samples 1, 2
IHC uses antibody panels to distinguish between different cancer types, such as p40 and TTF-1 to differentiate squamous cell carcinoma from adenocarcinoma in lung cancer 3
The College of American Pathologists suggests IHC detects protein overexpression that guides treatment decisions, most notably HER2 protein in breast cancer, where 3+ staining indicates eligibility for trastuzumab therapy 1
IHC quantifies estrogen receptor (ER) and progesterone receptor (PR) expression to determine endocrine therapy eligibility in breast cancer, with a recommended threshold of 1% positive tumor cells 4
Novel IHC markers like panTRK antibodies can screen for gene fusions with 95-97% sensitivity and 98-100% specificity, serving as a rapid, cost-effective initial test before molecular confirmation 5

The National Comprehensive Cancer Network recommends flow cytometry for diagnosing hematologic malignancies and establishing clonality, analyzing cell surface and intracellular markers on individual cells in suspension 9
Flow cytometry detects monoclonal B-cell populations by demonstrating kappa/lambda light chain restriction, which is diagnostic for chronic lymphocytic leukemia (CLL) when ≥5000 monoclonal B lymphocytes/mcL are present 9
A standard CLL/SLL panel includes CD19, CD20, CD5, CD23, CD10, kappa/lambda, with the typical CLL phenotype being CD5+, CD10−, CD19+, CD20 dim, surface immunoglobulin dim, CD23+ 9
Flow cytometry differentiates CLL from mantle cell lymphoma by demonstrating CD23 positivity and cyclin D1 negativity in CLL 9

The American Society of Clinical Oncology recommends FISH as the gold standard for confirming gene amplifications and translocations that guide cancer treatment, detecting specific DNA sequences and chromosomal abnormalities in both dividing and non-dividing cells 1, 9
FISH is the definitive test for HER2 status in breast cancer, with positive defined as HER2/CEP17 ratio ≥2.2 or average HER2 gene copy number ≥6 signals/nucleus 1, 2
FISH identifies del(11q), del(13q), trisomy 12, and del(17p) in CLL, which have major prognostic implications and guide treatment selection 9
FISH detects specific translocations like ETV6-NTRK3 in infantile fibrosarcoma and congenital mesoblastic nephroma with high specificity 5

The optimal approach uses IHC for initial screening, followed by FISH for confirmation of equivocal results or when treatment decisions require definitive molecular evidence, as recommended by the College of American Pathologists 1, 5
IHC provides rapid, cost-effective screening with high negative predictive value for clearly negative (0-1+) and positive (3+) cases, but FISH is necessary for equivocal results 1
FISH should be the initial test in specific contexts, such as HER2 testing in metastatic breast cancer or when IHC quality is questionable, as suggested by the American Society of Clinical Oncology 4
Next-generation sequencing may be more efficient than sequential single-gene FISH tests when multiple genetic alterations need evaluation, such as in adenocarcinoma requiring EGFR, ALK, ROS1, BRAF testing 5