Introduction

FISH technique is definitely one of the most convincing emerging technique for locating the specific DNA sequences, diagnosis of various genetic diseases and gene mapping. Recently, this technique is popularly being used for the identification of different oncogenes or different types of genetic aberrations that are responsible for causing various types of cancers. Not only it can help in diagnosis of different types of cancer but also it can provide additional information that may help to predict a patient’s outcome and if that person is likely to respond to various chemotherapy drugs.

In breast cancer, for example, a FISH test on the breast cancer tissue removed during biopsy can show whether the cells gave extra copies of the HER2/neu gene. Cells that have extra copies of the gene consequently have more HER2 receptors, which receive signals that stimulate the growth of breast cancer cells. So, such patients are more likely to respond to treatment with trastuzumab (Herceptin) which blocks ability of the HER2 receptors to receive growth signals (Jordan et al. 1999).

Working of FISH 

Different abnormalities that can be found in cancerous cells include:

1.  Deletion: In this type of abnormality, any part of the chromosome is observed to be missing.

2.  Translocation: In this type, any part of a chromosome detaches itself and then reattaches to different chromosome.

3.  Duplication: In this we find extra copies of chromosomes. The cell may contain numerous copies of a chromosome.

4.  Inversion: In this abnormality, a part of chromosome is in reverse order or 180° turned.

FISH tests are used in diagnosis of several types of cancers some of which include:

•     Breast cancer

•     Acute lymphoblastic leukemia (ALL)

•     Chronic lymphocytic leukemia (CLL)

•     Chronic/acute myeloid leukemia (CML/AML)

•     Myeloma

•     Prostate cancer

•     Lung cancer

•     Melanoma skin cancer

•     Ewings sarcoma

FISH analysis in solid tumors

1.  Lung cancer

Anaplastic lymphoma kinase (ALK) and echinoderm microtubule-associated protein-like 4 (EML4) gene rearrangements occur in approximately 5% of non-small-cell lung cancers (NSCLC), which lead to the overexpression of anaplastic lymphoma kinase and predict a response to the targeted inhibitor, crizotinib. Malignant pleural effusion is observed mostly among those having advanced lung cancer, and that too especially adenocarcinoma (Salido et al. 2011).

Ø Detection of ALK arrangement is possible with FISH technique and can detect number of fusion variants due to special structured probes.

2.  Ovarian cancer

It is a heterogeneous type of tumor, most of which include epithelial, germ cells and stromal cell tumors. It can be either low-grade endometroid cancer type I (gradual growth and beneficial prognosis) or high-grade non-endometroid cancer type II (fast progression and adverse response to treatment). Leading form of epithelial type is high-grade serous ovarian carcinoma (HGSOC). This can be due to mutations of TP53 gene or BRCA1 and BRCA2 genes or copy number alterations of CCNE1 (cyclin E1) gene (Mertens et al. 2016).

Ø Using FISH assessment of copy number of CCNE1 gene is done using a locus specific probe for a target gene located in 19q12 and a control region which is the centromere of the same chromosome (CEP19).

3.  Soft Tissues Sarcomas (STS)

These are uncommon cancers with a frequency of 3.58-6.1/100,000. Due to their complex biology, correct identification of tumor types is needed. The most commonly studied one includes Ewing sarcoma (ES), which is characterized by rearrangements of EWSR1 gene having many translocation factors like FLI1 (Fli-1 proto-oncogene) gene located in locus 11q24 (Asif et al. 2018).

Ø In these type of sarcomas, assessment of gene status is possible using a break apart probe and FISH technique. FISH testing based on recognition of gene arrangements or gene fusion allows pathological diagnosis, especially helpful in poorly differentiated sarcomas (Mertens et al. 2016).

4.  Breast cancer

As we are all aware of, breast cancer is the most frequent type of tumor identified in women. It is one of the main factors of mortality in the world with a five-year survival rate. The ERBB2 (erb-b2 receptor tyrosine kinase) gene, also called HER2, is a proto-oncogene coding for a cell receptor involved in signal pathways responsible for cell division and viability. Significant abnormality of this gene is the occurrence its extra copies defined as amplification (Slamon et al. 1989).

Ø The number of gene copies is assessed using the FISH or CISH technique. Personalized therapy can be used after the assessment of HER2 gene using one of the FDA-approved methods IHC, CISH or FISH. Treatments include inhibitors or humanized monoclonal antibodies like pertuzumab and trastuzumab.

Conclusion

The advancements have led to the use of FISH technique in diagnosis of various types of abnormalities and diseases including the most dangerous of all, cancer. Researches have shown that this technique has been successful not only in diagnosis of cancer but also in predicting its treatment, few of which have been discussed above. In comparison with other molecular profiling techniques, e.g., array-based comparative genomic hybridization, single nucleotide polymorphism (SNP), FISH is considered to be more straightforward, accurate and reliable.

References

Asif A, Mushtaq S, Hassan U, Akhtar N, Hussain M, Azam M, Qazi R (2018) Fluorescence in Situ Hybridization (FISH) for Differential Diagnosis of Soft Tissue Sarcomas. Asian Pac. J. Cancer Prev. APJCP, 19:655–660.

Huang WE, Stoecker K, Griffiths R, Newbold L, Daims H, Whiteley AS, Wagner M (2007) Raman FISH combining stable‐isotope raman spectroscopy and fluorescence in situ hybridization for the single cell analysis of identity and function. Environmental Microbiology, 9(8):1878–1889.

Jordan R, Edington J, Evans HH, Schwartz JL (1999) Detection of chromosome aberrations by FISH as a function of cell division cycle (harlequin-FISH). Biotechniques, 26:532-34.

Mertens F, Antonescu CR, Mitelman F (2016) Gene fusions in soft tissue tumors: recurrent and overlapping pathogenetic themes, The Journal of Pathology Clinical Research, 55: 291– 310.

O'connor C (2008) Fluorescence in situ hybridization (FISH). Nature Education, 1:171.

Salido M, Pijuan L, Martínez-Avilés L, Galván A.B, Cañadas I, Rovira A, Zanui M, Martínez A (2011) Increased ALK Gene Copy Number and Amplification Are Frequent in Non-Small Cell Lung Cancer. J. Thorac. Oncol. Off. Publ. Int. Assoc. Study Lung Cancer, 6:21–27. 

Slamon DJ, Godolphin W, Jones LA, Holt JA, Wong SG, Keith DE, Levin WJ, Stuart SG, Udove J, Ullrich A (1989) Studies of the HER-2/neu proto-oncogene in human breast and ovarian cancer. Science, 244:707-12.

Zwirglmaier K, Fichtl K, Ludwig W (2005) In situ functional gene analysis: recognition of individual genes by fluorescence in situ hybridization. Methods Enzymol., 397:338–51.