FISH test results for multiple myeloma list the specific chromosomal abnormalities found in your myeloma cells, and each one carries a different meaning for your prognosis and treatment plan. The report uses shorthand notation that can look like a foreign language, with terms like “del(17p)” or “t(4;14)” followed by percentages and gene names. Once you understand the basic vocabulary and know which findings are classified as high-risk versus standard-risk, your results become much more readable.
What a FISH Test Actually Detects
FISH stands for fluorescence in situ hybridization. The test uses fluorescent probes that attach to specific regions of chromosomes inside your myeloma cells, lighting up under a microscope so a technician can spot missing pieces, extra copies, or segments that have swapped places between chromosomes. It’s performed on a bone marrow sample, typically collected during a bone marrow biopsy.
Unlike standard chromosome analysis, FISH can detect abnormalities even when cells aren’t actively dividing. That matters because myeloma cells don’t always divide well in the lab. FISH is now considered essential for classifying myeloma risk and guiding treatment decisions. Preliminary results for key abnormalities like t(4;14) and 17p deletion are often available within 7 days, with a final report typically completed in about 14 days.
Decoding the Notation on Your Report
Your FISH report will contain a mix of letters, numbers, and parentheses. Here’s what each piece means:
- t (translocation): Two chromosomes have broken apart and swapped segments. Written as t(4;14), meaning parts of chromosome 4 and chromosome 14 traded places.
- del (deletion): A piece of a chromosome is missing. Written as del(17p), meaning the short arm of chromosome 17 has lost genetic material.
- p and q: These refer to the two arms of a chromosome. The “p” arm is the short arm, and the “q” arm is the long arm. So “17p” means the short arm of chromosome 17, and “1q” means the long arm of chromosome 1.
- + (gain): An extra copy of a chromosome or chromosome region is present. For example, +1q means there’s an additional copy of the long arm of chromosome 1.
- amp (amplification): Multiple extra copies of a region are present, going beyond a single gain.
You’ll also see gene names in parentheses after the notation, such as “t(4;14)(IGH/FGFR3 fusion)” or “del(17p)(TP53 loss).” These identify which specific genes are affected by the abnormality. The gene names help your oncologist understand what’s driving the myeloma at a molecular level.
Understanding Percentages and Cutoffs
Your report will include a percentage for each abnormality, representing how many of the examined cells carried that finding. Each abnormality has a laboratory cutoff below which the result is considered negative. For instance, the cutoff for del(17p) is around 3.4%, meaning the abnormality needs to appear in more than 3.4% of cells to count as a positive result. For t(4;14), the cutoff is roughly 6.8%, and for gain of 1q, it’s about 5.7%. If your percentage falls below the cutoff, the report will list that abnormality as “negative” or “not detected” even though a small number of cells showed the signal.
Labs typically enrich the bone marrow sample to concentrate plasma cells (myeloma cells) before running FISH. This sorting step improves accuracy, since testing unsorted marrow could dilute the myeloma signal with normal cells and miss real abnormalities.
High-Risk Abnormalities
The abnormalities that matter most are the ones classified as high-risk, because they signal more aggressive disease and influence which treatments your doctor recommends. The current list of high-risk cytogenetic abnormalities includes:
- del(17p): Deletion of the short arm of chromosome 17, which removes the TP53 tumor suppressor gene. This is the single most impactful abnormality. Even on its own, del(17p) is enough to classify the disease as high-risk.
- t(4;14): A translocation between chromosomes 4 and 14. Widely accepted as a high-risk marker.
- t(14;16): A translocation between chromosomes 14 and 16. Its independent impact has been debated, but when combined with other high-risk abnormalities, it’s associated with particularly aggressive disease. Patients with both del(17p) and t(14;16) had a median overall survival of about 33.5 months compared to 62.4 months for those with del(17p) alone.
- t(14;20): A rarer translocation between chromosomes 14 and 20.
- Gain or amplification of 1q: Extra copies of the long arm of chromosome 1. Your report may describe this as “1q21x3” (gain, meaning 3 total copies) or “1q21x4” or higher (amplification, meaning 4 or more total copies). Amplification of 1q is uniformly associated with poor survival and is increasingly treated as a definitive high-risk finding.
- del(1p): Deletion of the short arm of chromosome 1, involving loss of the CDKN2C gene.
Double-Hit and Triple-Hit Myeloma
If your report shows two of these high-risk abnormalities together, your disease may be classified as “double-hit” myeloma. Three or more high-risk findings is called “triple-hit.” These categories carry a worse prognosis than a single high-risk abnormality and typically lead to more intensive treatment approaches.
Standard-Risk Findings
Not every abnormality on a FISH report is bad news. Some findings place you in the standard-risk category, which is associated with better outcomes and longer remissions.
Hyperdiploidy is the most common standard-risk finding. It means the myeloma cells contain extra whole chromosomes, typically between 48 and 74 total (normal cells have 46). FISH reports show this as trisomies, or gains of specific odd-numbered chromosomes like 3, 5, 7, 9, 11, 15, and 19. Hyperdiploid myeloma tends to lack the aggressive translocations and chromosome 13 abnormalities seen in non-hyperdiploid disease.
The translocation t(11;14), a swap between chromosomes 11 and 14, appears in roughly 15% to 25% of myeloma cases. It has historically carried a prognosis similar to the general myeloma population, placing it in the standard-risk category. However, t(11;14) has taken on new importance because it identifies patients who may respond to a targeted therapy called venetoclax. Myeloma cells with this translocation tend to depend heavily on a specific survival protein, and venetoclax blocks that protein. Early trials showed meaningful single-agent activity in relapsed patients with t(11;14), and investigation in this group is ongoing.
How to Put It All Together
When you read your FISH report, the practical question is: does it contain any of the high-risk abnormalities, and if so, how many? A report that shows only hyperdiploidy or t(11;14) with no high-risk markers is a favorable result. A report showing one high-risk abnormality means your treatment plan will likely be more aggressive than standard-risk protocols. Two or more high-risk abnormalities calls for even more intensive management.
Your FISH results also feed into the Revised International Staging System, which combines cytogenetic findings with blood markers like LDH levels and albumin to assign an overall stage. So your FISH report isn’t the whole picture, but it’s one of the most important pieces.
Why FISH Results Can Change Over Time
One thing that catches many patients off guard is that FISH results aren’t permanent. Myeloma evolves. The proportion of patients with high-risk cytogenetic features was 33% at diagnosis in one study but rose to 49% at relapse, largely because new 17p deletions emerged over time. The clonal makeup of myeloma can shift dramatically: subclones can grow, shrink, disappear, or acquire entirely new abnormalities.
This is why doctors often repeat FISH testing if the disease relapses or stops responding to treatment. The abnormalities present at relapse actually predicted survival more strongly than those found at diagnosis, with high-risk features at relapse carrying roughly double the risk of death compared to high-risk features that were only present at diagnosis. Your treatment plan after relapse should be guided by the most recent FISH results, not the original ones.