Why the “Same Cell” Matters

Each technique contributes different evidence, but parallel slides introduce uncertainty. Cells can be lost during preparation, the abnormal population can be unevenly distributed, and serial tissue sections do not contain identical cellular profiles. A 2022 technical study summarized the problem clearly: analysis on different slides "does not permit comparison of staining at the single cell level" (Morrison et al., 2022).

Target FISH changes the unit of correlation from the region or cell population to the individual cell. The reviewer can ask: Is this morphologically suspicious plasma cell also positive for the genomic abnormality? Does this immunoreactive rare cell carry the expected FISH pattern? Are the FISH-positive cells the same cells that expressed the protein marker?

That is more than a visual convenience. It helps protect specificity when the cells of interest are rare or mixed with non-neoplastic cells.

How the Target FISH Workflow Works

Target FISH is the automated matching of Giemsa + FISH, IHC + FISH, or immunofluorescence + FISH, with unassisted cell relocation and side-by-side presentation. Unlike an overlay inferred from adjacent sections, this process returns to the cells previously imaged on the exact same slide.

The exact laboratory protocol depends on specimen type, stain, probe, and the laboratory's validated procedure. The core workflow is sequential:

1. Target Identification: Cells are first stained with Giemsa, IHC, or immunofluorescence. Morphologically or phenotypically relevant cells are detected and imaged.
2. Coordinate Recording: Automated imaging preserves the coordinates and image data for selected cells or regions of interest.
3. FISH Processing: The same slide is processed for FISH. The initial stain may be removed or otherwise processed according to the validated protocol, followed by probe hybridization.
4. Cell Relocation: The system returns to the recorded coordinates and acquires the FISH channels from the same cells.
5. Side-by-Side Review: The original morphology or immunostain image is matched with the corresponding FISH image for interpretation, documentation, and reporting.

Multiple Myeloma: A Natural Use Case for Morphology-FISH Correlation

Multiple myeloma illustrates the diagnostic problem especially well. Plasma cells often represent a minority of nucleated cells in a bone marrow aspirate, and their distribution can be patchy. Direct FISH on an unselected marrow population can dilute the abnormal clone and produce a false-negative or misleadingly low abnormal-cell fraction.

Current guidance reflects that risk and recommends plasma-cell enrichment for all myeloma FISH samples "to minimize the potential for `false-negative' test results" (Lu et al., 2025). The guidelines discuss CD138 magnetic enrichment and flow sorting as common approaches, while also noting the effects of specimen volume, plasma-cell concentration, time to processing, and marker stability.

Target FISH takes a different route: it selects the cells for analysis through morphology or phenotype and then evaluates FISH signals specifically in those cells.

In a 40-patient plasma-cell myeloma series using the BioView platform, plasma cells were May-Gr］wald-Giemsa stained and imaged, the slides were de-stained and hybridized, and the previously identified cells were relocated for FISH analysis. The authors described the principal benefit as "complete certainty that the cytogenetic abnormality was detected in the cells of interest" (Ma et al., 2016). The study evaluated TP53/CEP17, IGH/FGFR3, IGH/MAF, and 1q21/1p32 probe sets and demonstrated the feasibility of integrating morphologic identification with automated FISH review.

IHC + FISH: Connecting Protein Expression with Genomic Status

IHC and FISH answer different biological questions. IHC shows the presence, localization, and relative expression of a protein. FISH interrogates defined DNA or RNA targets. When the two measurements are made in the same cells, the laboratory can evaluate whether phenotype and genotype are concordant within a heterogeneous population.

Potential applications include:

• Confirming that a genomic abnormality is present in cells expressing a lineage or tumor marker.
• Investigating protein-gene discordance within a mixed or heterogeneous tumor population.
• Characterizing rare cells after immunostaining without losing their spatial identity.
• Linking copy-number or rearrangement status to a defined cellular phenotype in translational research.
• Preserving limited cytology material by obtaining sequential information from one preparation.

These possibilities do not make IHC and FISH interchangeable. Nor do they mean every observed association is clinically actionable. The value lies in strengthening cell attribution: the protein and genomic findings can be assigned to the same object under review.

Giemsa + FISH: Keeping Genomic Results Anchored to Morphology

Giemsa-stained preparations remain central to hematopathology because morphology carries information that a fluorescence signal alone cannot provide. Nuclear shape, chromatin pattern, cytoplasmic characteristics, and cellular context help distinguish the relevant population from background cells.

By recording the Giemsa appearance before hybridization and relocating those cells afterward, Target FISH lets the reviewer retain that morphological context while interpreting the genomic signal. In myeloma, this means FISH can be scored specifically in plasma cells selected by their appearance. In other hematologic or cytologic settings, the same principle can be used to focus analysis on atypical, suspicious, or rare cells, subject to local validation and the platform's intended-use requirements.

What Laboratories Should Validate

Same-cell matching removes one important source of uncertainty, but it creates a multi-stage assay that must be validated as an integrated workflow. Laboratories should examine:

• Cell recovery and relocation success after sequential processing.
• Stability of the initial stain or immunophenotypic signal before image capture.
• Preservation of nuclear morphology and FISH signal quality after de-staining and hybridization.
• The minimum number of target cells needed for an informative result.
• Reviewer agreement on target-cell selection and FISH classification.
• Normal reference ranges and assay-specific cutoffs.
• Failure modes caused by low cellularity, cell detachment, slide aging, background fluorescence, or coordinate mismatch.
• Image retention, audit trail, result review, and report language.

The distinction between analytical targeting and physical enrichment should also be explicit. Target FISH directs analysis to pre-identified cells on the slide; magnetic or flow-based enrichment changes the cellular composition before analysis. The best choice depends on specimen quality, available cell count, laboratory infrastructure, and the clinical question. Some laboratories may use these approaches as alternatives, while others may find them complementary.

From Three Separate Answers to One Cellular Narrative

Laboratories routinely integrate morphology, phenotype, and genotype in their final interpretation. The limitation is that the underlying data may originate from different cells, slides, or tissue levels. Target FISH makes that integration literal. A cell can first be recognized by Giemsa morphology or an IHC/IF marker, then relocated after hybridization, with the corresponding FISH result displayed beside its original image.

BioView's distinctive contribution is not simply automated FISH capture; it is preserving cellular identity across sequential staining sessions.

For laboratories working with rare cells, heterogeneous marrow, cytology specimens, or phenotype-genotype questions, that capability provides a precise answer to a deceptively simple question: Are we looking at the same cell?