IHC stain only S100 Protein

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Tumor marker staining.

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IHC Stain Only S100 Protein - Comprehensive Medical Test Guide

Why is it done?
- Detects S100 protein expression in tissue samples using immunohistochemical staining methodology to identify specific cell types and diagnose various neoplastic and non-neoplastic conditions
- Diagnostic purposes for melanoma and other melanocytic lesions; differentiation of benign versus malignant skin lesions
- Identification of neural and neural crest-derived tumors including neurofibromas, schwannomas, and other nerve sheath tumors
- Classification of lymphomas and assessment of langerhans cell histiocytosis
- Performed when histologic diagnosis is uncertain or requires confirmation; typically conducted during initial pathologic examination of biopsied or resected tissue
- Part of comprehensive immunohistochemical panel to establish definitive diagnosis and guide treatment decisions
Normal Range
- Negative Result (Normal): No immunohistochemical staining or minimal/absent S100 protein expression in the tissue specimen
- Positive Result (Abnormal): Presence of S100 protein demonstrated by brown chromogenic staining in tissue cells; intensity scored as weak (+), moderate (++), or strong (+++)
- Units of Measurement: Qualitative (Present/Absent) with semi-quantitative scoring: negative, weakly positive, moderately positive, strongly positive
- Interpretation Guidelines: Negative S100 staining does not necessarily exclude melanoma or melanocytic lesions; positive staining suggests melanoma, neural tumors, or other S100-positive neoplasms depending on morphologic context
- Distribution Pattern: Diffuse staining throughout lesion versus focal or peripheral staining may indicate different diagnoses and requires correlation with histomorphology
Interpretation
- Positive S100 Staining Indicates: Presence of S100-expressing cells consistent with melanoma, benign nevi, nerve sheath tumors, langerhans cell histiocytosis, or certain lymphomas; high sensitivity but moderate specificity for melanoma
- Negative S100 Staining Indicates: Absence of S100-positive cells; does not exclude melanoma as 5-10% of melanomas may be S100-negative, suggesting non-melanoma diagnosis or need for additional immunohistochemical markers
- Staining Intensity Assessment: Strong diffuse staining highly suggestive of melanoma or schwannoma; weak or focal staining requires correlation with morphology and additional markers; pattern helps differentiate benign nevi from melanoma
- Distribution Patterns: Maturation (superficial strong, deep weak) suggests benign nevus; absence of maturation suggests melanoma; involvement of deep dermis or subcutis indicates malignancy risk
- Factors Affecting Results: Tissue fixation quality and duration, antigen retrieval technique, antibody specificity, presence of background melanin, crush artifact, and prior chemotherapy may affect staining intensity and interpretation
- Clinical Correlation Essential: S100 alone cannot diagnose melanoma; must be interpreted in context of histomorphology, clinical presentation, and results of additional immunohistochemical markers (Melan-A, HMB-45, SOX10, Mitf)
- Diagnostic Implications: Helps establish diagnosis of melanoma versus other malignancies; assists in classification of neural tumors; supports identification of specific lymphoma subtypes; may guide prognosis and treatment decisions
Associated Organs
- Primary Organ Systems: Skin and integumentary system (primary site of melanoma); nervous system (nerve sheath tumors, neuroblastoma); lymphatic system (lymphomas); bone and soft tissue (sarcomas)
- Melanocytic Lesions: Cutaneous and mucosal melanomas (primary and metastatic); benign nevi; acral lentiginous melanoma; uveal melanoma; acanthoma (S100-positive variant)
- Neural Tumors: Schwannoma (neurilemoma), neurofibromas, malignant peripheral nerve sheath tumors (MPNST), neuroblastoma, nerve sheath sarcoma, granular cell tumor
- Hematologic and Histologic Disorders: Langerhans cell histiocytosis, certain lymphomas (particularly lymphoblastic lymphoma), clear cell sarcoma, solitary fibrous tumor
- Associated Medical Complications: Melanoma metastasis to regional lymph nodes, distant organs, and brain; neural tumors causing compression or neurologic deficits; systemic complications from lymphoma; recurrence and progression
- Prognosis Implications: S100-positive melanomas may correlate with different survival outcomes; neural tumors positive for S100 may indicate specific subtypes with different prognosis; helps stratify risk and guide surveillance protocols
Follow-up Tests
- Complementary Immunohistochemical Markers: Melan-A/MART-1 (melanoma marker with higher specificity), HMB-45 (gp100, helpful for epithelioid melanomas), SOX10 (sensitive for melanoma and neural tumors), Mitf, TRP-1, and Ki-67 (proliferation index)
- Additional Tests for S100-Positive Lesions: Molecular testing (BRAF V600E, NRAS, KIT mutations in melanoma); fluorescence in situ hybridization (FISH) for gene amplification; flow cytometry if lymphoma suspected
- Staging and Metastatic Workup: Chest X-ray or CT chest/abdomen/pelvis; PET/CT scan for high-risk melanomas; brain MRI for melanomas with concerning features; sentinel lymph node biopsy; additional imaging based on stage
- Clinical and Laboratory Monitoring: Serum LDH (prognostic marker in melanoma); regular dermatologic examination; lymph node surveillance; repeat imaging per established protocols based on stage and risk factors
- Monitoring Frequency: Clinical examination every 3-12 months depending on stage; imaging surveillance for stage IIC and higher melanomas; annual follow-up for lower-risk lesions; lifetime monitoring for melanoma given recurrence risk
- Related Diagnostic Tests: Histopathology review, complete blood count, comprehensive metabolic panel, immunophenotyping for lymphomas, genetic testing for familial melanoma syndromes (CDKN2A mutations)
Fasting Required?
- Fasting Requirement: No - Fasting is NOT required for IHC S100 protein staining
- Reason: IHC staining is performed on tissue samples (biopsy or surgical specimens) obtained through skin biopsy, surgical excision, or other tissue procurement procedures - not blood tests, therefore fasting status is irrelevant
- Patient Preparation Instructions: If undergoing biopsy procedure to obtain tissue sample: arrive on time; wear comfortable, loose clothing for easy access to biopsy site; bring photo ID and insurance information; arrange transportation if local anesthesia will be used
- Pre-Procedure Considerations: Discontinue aspirin or NSAIDs 5-7 days prior to biopsy if possible (consult with physician); inform providers of bleeding disorders or anticoagulation therapy; avoid topical medications on biopsy area; clean skin with gentle soap
- Post-Procedure Care: Keep biopsy site clean and dry; follow wound care instructions provided by physician; avoid strenuous activity; watch for signs of infection; take prescribed pain medication if needed; attend follow-up appointments
- Results Timeline: IHC staining typically completed within 5-10 business days; results may be available sooner for expedited cases; pathologist reviews slides and issues comprehensive report with interpretation and recommendations

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