CELL BLOCK and its diagnostic utility in histopathology
- 1. Cell Block & Its Diagnostic Utility BY DR. SAMEEKSHA SHARMA DNB PATHOLOGY
- 4. What is a cell block • A cell block is a method of preparing cytologic material so that it can be processed, sectioned, stained, and viewed as a histology section. • It can provide diagnostic information in addition to that obtained from cytology slides. • It is easier to do special stains, and immunohistochemistry on cell block slides rather than on regular cytology slides because the slides often require adaptations of the staining protocols and different controls.
- 6. NEED FOR CELL BLOCK • Acquisition of tissue for cell block can increase both diagnostic sensitivity and specificity (through both cellular morphology and ancillary testing) • It requires minimal effort and is extremely cost efficient. • Moreover, tissue preserved in cell block can be readily shared for second opinions and research without fear of losing the original diagnostic smear specimen.
- 8. METHODS OF CELL BLOCK PREPARATION • Direct processing of tissue fragments present in fluids. • Plasma thrombin method • Fixed sediment method • Bacterial agar method • Technique using alcohol, acetone and paraffin • Compact technique • Cell blocks from Millipore • Histogel method • Gelatine embedding • Collodion bag method • Scraping of cytology smears • Automated preparation • Albumin method
- 12. PLASMA-THROMBIN METHOD • PRINCIPAL: to enmesh the cellular material in a clot. • Very simple and cost effective method. • DISADVANTAGES of this technique include: • An inability to control clot formation and irregular distribution of cells within the pellet, but these can be overcome by constant agitation. • Some thromboplastin agents contain epithelial cells that may interfere not only with diagnosis but also with interpretation of ancillary studies.
- 19. CELL BLOCKS: FIXATION • SALINE: provides flexibility to submit for cultures, flow cytometry, and liquid based cytology • But cell integrity is compromised even over limited periods. • A sample processed within 1 to 24 hours following collection in saline negatively and significantly impacts preservation, thereby compromising architectural and cytological detail (e.g. lyses the cells), possibly because saline is not perfectly isotonic with the cell cytoplasm.
- 20. • RPMI: it is ideal for supporting cultures and leukocytes • Especially when considering a suspected lympho - proliferative disorder. • But it is not readily available at point of collection, partly because it needs to be refrigerated.
- 21. CELL BLOCK FIXATION AND PROCESSING • Formalin fixation – formalin has been used to fix cell blocks from FNA rinses and has been claimed as ‘the poor man’s cell blocks as it does not require any special equipment or reagents. • Alcohol fixation – the cellient system uses methanol as a fixative. Although immunostains and molecular analysis may be performed on samples fixed in alcohol, the laboratory needs to validate tests appropriately to avoid false negative or false positive results in IHC.
- 22. • Nathan alcohol formalin substitute (NAFS) fixation – a cellblock technique using an ethanol- formalin fixative (nine parts of 100% ethanol and one part of 40% formaldehyde), followed by paraffin processing, has been used to obtain good cytological details with less toxicity. • Microwave fixation – microwave fixation can expedite the overall process of cell block preparation and can reduce the turnaround time significantly.
- 23. ADVANTAGES OF CELL BLOCK • Slides are more readily interpretable by histopathologists. • Availability of a block facilitates more sections. • Important residual material is salvaged which is generally not available in cytology smears. Loose cells, cell aggregates and microscopic tissue fragments are easily recoverable. • Concentrated in a small area of the slide so examination less time consuming. • Special stains mucicarmine, Congo stain, melanin etc. • Stains for immunohistochemistry
- 24. • Most ancillary testing platforms are developed on formalin- fixed paraffin-embedded (FFPE) tissue. • So cell blocks processed in this way generally do not require additional validation, and when performing immunostaining, the same slides serve as controls for surgical specimens and cell blocks.
- 25. • For microorganisms especially fungi and bacteria • Pattern and architectural recognition of tumor possible • Cell block is simple, reproducible and readily available in routine laboratory • No necessity of biopsy • Storage of cell blocks is easier than unstained slides
- 26. DISADVANTAGES • Compared to routine smears takes longer time • They are not always sufficient • The risk of losing cytological material during tissue processing or sectioning is another drawback because of the small size of the specimen. • Sparse cellularity • Distortion artefacts • It is skill dependant and labour- intensive and demanding. • As compare to traditional smear cytology, the CB method adds an extra cost to patient management.
- 27. CELL BLOCKS IN BODY FLUIDS • Cytologic studies of body fluids are done to ascertain the etiology of effusion. • Cytologic evaluation is the best method to detect malignancy in the body cavity fluids. • Diagnostic accuracy of routine smears for malignancy ranges from 50-80% with a false negative rate of about 25%. To improve diagnostic accuracy, cell block preparation can be done.
- 28. Few advantages • Spontaneous formed clot in the body fluid may enmesh virtually all cells. • Induced clot prepared from the sediment obtained by centrifugation of the fluid specimen would also contain many cells. • Identification of primary site of malignancy can be enhanced with the use of cell block technique. • Histologic patterns of cancer (acinar, papillary, duct like) can be readily identified on a cell block.
- 29. • Psammoma bodies, granulation tissue, cholesterol clefts, microorganism fragments of collagenous stroma, hyperplastic mesothelium, etc can be identified. • Fluid samples or tissue fragments can be preserved in a refrigerator for 72 hrs before processing in cell blocks. • IHC on cell blocks are comparable to that of surgical specimens (differentiation of reactive mesothelial cells clusters from metastatic adenocarcinoma and mesothelioma). • Microarray technique, molecular tests like FISH, in situ PCR. • Electron microscopy.
- 30. ROLE OF CELL BLOCK IN NON NEOPLASTIC EFFUSION • Reactive mesothelial cells • Differentiation between polymorphous lymphocytes of non neoplastic effusion & monomorphous lymphoid cells of lymphoproliferative disease. • Rheumatic effusion (elongated & giant cell multinucleated histiocytes, granular background, cholestrol crystals) • LE cells, granulomas in TB, number of parasitic, fungal and viral diseases can be picked up.
- 31. CELL BLOCK IN IHC AND MOLECULAR ANALYSIS • Cell blocks are the preferred choice for ICC as they are comparable with surgical biopsies, can use the same control slides, provide the best milieu for morphological interpretation and are without background staining. • Avoids subjecting patients to unnecessary sampling. • Biopsy tissue is not available • Cell block is preferable to a biopsy for molecular testing as the ratio of tumor to background cells is usually high
- 32. GYNAECOLOGICAL CYTOLOGY • With the advent of liquid based collections, the opportunity for cell block preparation is now available because a residual specimen is almost always present. • The occasional presence of stromal invasion and tumor necrosis in cell block sections is useful for differentiating HSIL from squamous cell carcinoma in cervical cytology. • ICC of p16INK4a, a surrogate marker of human papilloma virus infection, and ISH studies for HPV can be performed on Cell blocks.
- 33. • THYROID – minimal role of cell block because of low cellularity • Direct smears in combination with liquid based cytology are preferred. • BREAST – cell block is considered to be suitable, with some reservations, for the assessment of hormone receptors and Her- 2/neu IHC staining. • Alcohol fixation may also alter the antigenicity of progesterone receptors.
- 34. LUNG • The role of cell block has also been highlighted in the sub typing of lung carcinoma by morphology and IHC for squamous and adenocarcinoma markers. • Cell blocks can be prepared from samples from endobronchial ultrasound- guided transbronchial needle aspirates, and subjected to a panel of antibodies.
- 35. CYTOLOGICAL MICROARRAY USING CELL BLOCKS • Similar to tissue microarrays, cell blocks of FNA material or effusion fluids have been increasingly used for array construction for immunohistohemical marker validation. More recently, cultured cells have been used to make cell blocks for array construction. Although technically complex and expensive, their immense role in clinical research make cell block microarrays a potentially useful tool in cytology.