ABPath Anatomic Pathology cheat sheet

Breast conservation for DCIS: a margin threshold of 2 mm is associated with lower ipsilateral recurrence; for invasive carcinoma, 'no tumor on ink' defines a negative margin.

Colorectal carcinoma resection: evaluate at least 12 regional lymph nodes for adequate staging; report tumor deposits, extramural venous invasion, and peritoneal involvement.

Pancreaticoduodenectomy for ductal adenocarcinoma: a margin is positive (R1) when tumor is within 1 mm of the transection or dissection margin.

Cutaneous melanoma: Breslow thickness drives T stage and excision margins; report ulceration, mitotic rate for thin lesions, and microsatellites.

Prostatectomy: Grade Group 1 equals Gleason 3+3; seminal vesicle invasion is pT3b; a positive margin is tumor at ink, not merely close.

Frozen section is best for margin status, nodal metastasis, and tissue adequacy; it is unreliable for distinguishing benign from malignant follicular thyroid lesions and for fat margins.

Lung adenocarcinoma: report invasive size, lepidic pattern, spread through air spaces, pleural invasion, and nodal station; IASLC grading uses predominant and high-grade patterns.

Thyroid papillary carcinoma: diagnosis rests on nuclear features such as enlargement, clearing, grooves, and pseudoinclusions, not architecture alone; report extrathyroidal extension and margin.

Thyroid FNA uses the Bethesda System categories I through VI; category VI carries the highest risk of malignancy, while category II is benign.

Salivary gland FNA uses the Milan System; suspicious and malignant categories generally prompt resection, whereas the benign category has low risk.

Serous effusion: adenocarcinoma is favored by Ber-EP4, MOC-31, and claudin-4; mesothelioma by calretinin, WT1, D2-40, and CK5/6.

EBUS-TBNA of mediastinal nodes: combine cytology with cell block immunohistochemistry; p40 supports squamous carcinoma, while TTF-1 and napsin A support lung adenocarcinoma.

Cervical cytology: high-risk HPV testing is used for ASC-US triage and cotesting; p16/Ki-67 dual stain improves specificity for high-grade lesions.

Urine cytology Paris System: report high-grade urothelial carcinoma, atypical urothelial cells, and suspicious for high-grade; low-grade lesions are not reliably graded.

FNA adequacy depends on cellularity and lesional representation; rapid on-site evaluation improves adequacy and triage for ancillary studies.

Pancreaticobiliary cytology: report negative, atypical, suspicious, and positive; a positive result usually requires malignancy, while atypical results need clinicopathologic correlation.

Cause of death is the disease or injury that initiates the fatal sequence; mechanism is the physiologic derangement, and manner is natural, accident, suicide, homicide, or undetermined.

Postmortem lividity fixes after roughly 6 to 12 hours; rigor mortis begins in small muscles and resolves after about 24 to 48 hours; temperature modifies both.

Pulmonary thromboembolism from deep vein thrombosis is a common cause of sudden death; examine the leg veins and pulmonary arteries at autopsy.

Perinatal autopsy: examine the placenta and cord, obtain radiographs and karyotype when indicated, and assess for congenital anomalies and infection.

Gunshot wounds: soot and stippling indicate close-range discharge; exit wounds generally lack soot and may be larger and more irregular.

Aortic dissection causes death by rupture, tamponade, or branch occlusion; identify the intimal tear and assess the true and false lumens.

Autopsy sampling should include representative sections of all major organs and lesions; brain fixation improves sectioning for neurodegenerative disease.

Postmortem vitreous chemistry can help estimate time since death and assess electrolyte abnormalities; interpret with temperature and decomposition.

HER2 IHC breast: 3+ is positive, 2+ is equivocal and requires ISH; ISH is positive when the HER2/CEP17 ratio is at least 2.0 or HER2 copies are at least 6.0 per cell.

Mismatch repair IHC: loss of MLH1 and PMS2 suggests MLH1 abnormality; BRAF V600E or MLH1 promoter methylation testing distinguishes sporadic from Lynch syndrome.

NSCLC predictive markers include EGFR mutations, ALK and ROS1 rearrangements, BRAF V600E, MET exon 14, RET, and PD-L1; test before targeted therapy.

Cytokeratin profile: CK7 positive/CK20 negative favors lung, breast, ovary, and thyroid; CK7 negative/CK20 positive favors colorectal; CK7 and CK20 positive favors urothelial and gastric.

Electron microscopy: desmosomes and tonofilaments support squamous differentiation; melanosomes support melanoma; dense-core granules support neuroendocrine tumors.

FISH break-apart probes: a normal signal is fused; separation of 5-prime and 3-prime signals indicates rearrangement; interpret with copy number and background.

Molecular testing requires a validated limit of detection and variant allele frequency; low tumor cellularity can cause false-negative results.

PD-L1 scoring: TPS is the percentage of viable tumor cells with membranous staining; CPS includes tumor and immune cells divided by viable tumor cells times 100.

CLIA requires laboratories to perform proficiency testing, quality control, and validation before reporting patient results.

CAP laboratory accreditation uses checklists and peer inspections; deficiencies are classified and require corrective action.

Turnaround time is measured from specimen receipt to report release; monitor preanalytical, analytical, and postanalytical errors separately.

Laboratory information systems exchange orders and results using HL7; FHIR is a newer standard for interoperability using resources and web APIs.

Validation of a new IHC assay includes sensitivity, specificity, concordance, and reproducibility; documentation must be retained for inspection.

Biosafety: formalin and xylene require ventilation; sharps and fresh tissue require BSL-2 practices and appropriate personal protective equipment.

Digital pathology validation should include concordance with glass slides, image quality, and cybersecurity safeguards.

Root cause analysis distinguishes active errors from latent system failures; corrective action should address the system, not only the individual.