7.3 Diagnostic Testing, Staging, and Prognosis

Diagnosis on CPHON is a sequence, not a single scan. TCO II.A.4–5 items test whether you can open the right labs, get a child safely through sedation and a needle, pick imaging that matches the compartment, and explain what a stage and a risk group are for—without dumping every cooperative-group table into a family's first hour. Histology, cytogenetics, and measurable residual disease (MRD) then turn a name into a prognosis. Your job includes the sentence families remember: treatment started, and we are still waiting on cytogenetics.

Labs that belong on the new-diagnosis clipboard

Start with a CBC and peripheral smear. Cytopenias, circulating blasts, and schistocytes change urgency. Chemistries for a suspected hematopoietic or bulky embryonal cancer are a TLS panel: potassium, phosphate, calcium, uric acid, LDH, and creatinine. High potassium and phosphate with falling calcium and rising uric acid is lysis, not a dietary oddity. Coagulation studies (PT, PTT, fibrinogen) catch DIC, especially when APL is possible. Type and screen before invasive procedures and before you might need platelets or red cells.

Add viral serologies (for example hepatitis, HIV, CMV, EBV, varicella) as the protocol and transplant path require—results matter before immunosuppression and before live-virus issues. Tumor markers are not universal. Alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (β-hCG) belong to suspected germ-cell tumor and hepatoblastoma workups. Catecholamine metabolites (homovanillic acid and vanillylmandelic acid) belong to suspected neuroblastoma. Do not send AFP because it is oncology. A 15-year-old with a distal femoral mass needs osteosarcoma staging, not a reflex pregnancy-tumor marker panel unless the differential includes germ-cell disease.

A 4-year-old with fever, pallor, and a high LDH gets the TLS chemistries before the first steroid dose, not after. A teenager with gingival oozing and a possible APL picture gets fibrinogen and products in the room before the diagnostic marrow, not a casual send-whenever laboratory round.

Procedures: NPO, sedation, counts, and coagulopathy

Bone marrow aspirate and biopsy diagnose leukemia and stage some solid tumors (neuroblastoma, Ewing sarcoma on many protocols). Lumbar puncture with IT chemotherapy stages ALL and lymphoma CNS disease and starts sanctuary therapy. Tumor biopsy belongs to the treating surgical or interventional team so the tract sits in a future resection field. Central line placement is both access and a procedure with bleeding risk.

Safety is protocol, not toughness. Keep the child NPO per anesthesia. Review last meal, last breast milk or formula, and last clear. Sedation safety means airway assessment—never casual sedation of a child with a mediastinal mass who cannot lie flat. Correct coagulopathy and raise platelets to the protocol threshold before marrow, LP, or line insertion. A platelet count of 12,000/µL is not a quick-LP situation. Hold anticoagulants as ordered. Verify type and screen and product availability. After LP with IT methotrexate, watch for post-LP headache, but also for the wrong-route disaster: vincristine is never intrathecal. That check is a diagnostic-day nursing behavior, not only a chemotherapy-chapter trivia item.

A 3-year-old booked for diagnostic LP, marrow, and port placement in one anesthesia needs one NPO clock, one airway plan, platelet and coag clearance, and a time-out that names each IT drug. If the PT is still prolonged and fibrinogen is low, the OR wait is a safety action, not a delay of diagnosis for its own sake.

Imaging that matches the compartment

Ultrasound is the first look at an abdominal mass in a preschooler—fast, no ionizing radiation, good for kidney versus adrenal versus liver. CT maps chest nodules (osteosarcoma, Wilms tumor lungs) and some abdominal extent. MRI is the CNS and bone-marrow-extent study; it is also preferred for many pelvic and extremity sarcomas. PET assesses metabolically active disease in selected lymphomas and sarcomas. MIBG (metaiodobenzylguanidine) scan is the neuroblastoma avidity study. Bone scan hunts osteosarcoma skip lesions and clear-cell sarcoma of kidney bone metastases. Do not send every new leukemia to MIBG, and do not skip chest CT in osteosarcoma because the child is breathing fine.

Radiation exposure is not zero in children. That is why ultrasound and MRI are preferred when they answer the question. It is not a reason to skip a needed chest CT for pulmonary metastases. A 3-year-old with a flank mass starts with ultrasound; a 14-year-old with a distal femoral lesion needs dedicated bone MRI plus chest CT, not a babygram.

What stage is for—disease-specific tools, not one adult TNM

Stage (or risk group) is a language for how much disease is where, so teams assign treatment intensity and talk prognosis. Pediatric oncology does not use one adult AJCC sticker for every diagnosis.

• ALL CNS-1 / CNS-2 / CNS-3: CNS-1 is no blasts in CSF. CNS-2 is blasts with CSF WBC under 5/µL. CNS-3 is blasts with CSF WBC 5/µL or higher, or clinical CNS disease (cranial-nerve palsy, hypothalamic mass). CNS status changes IT intensity and sometimes radiation—not a hallway nickname.
• Murphy–St. Jude staging for pediatric NHL: extent of nodal and extranodal disease, including whether marrow or CNS is involved. It is why a huge unresectable abdominal Burkitt lymphoma is not stage I because it started in one organ.
• INRG for neuroblastoma: image-defined risk factors and metastatic pattern (L1, L2, M, MS) plus age and biology such as MYCN. It is a risk classifier, not adult stage IV.
• PRETEXT for hepatoblastoma: how many liver sections are involved before therapy, plus extrahepatic annotations. It answers resectability versus chemotherapy first.
• IRS grouping for rhabdomyosarcoma: residual disease after initial surgery (complete resection, microscopic residual, gross residual, metastatic). Biopsy-only versus primary resection changes group.
• AJCC / surgical staging for osteosarcoma: local extent plus skip metastases and lungs. Surgery defines margins; chest CT defines the metastatic conversation.

Do not dump the entire tables. Teach that the wrong staging language is a teaching error: calling neuroblastoma T3N1M1 because someone memorized adult lung-cancer TNM does not help a parent. Stage is a treatment-intensity tool, not a room assignment on the unit.

Histology, cytogenetics, and MRD as prognosis

Histology (favorable versus anaplastic Wilms tumor; embryonal versus alveolar rhabdomyosarcoma; APL versus other AML) still matters. Cytogenetics and molecular results then overlay risk and targeted therapy, as the previous section taught. MRD is the deepest response measure in ALL and is used in other diseases on protocol: flow cytometry or molecular methods detect leftover disease below a morphologic 5% blast threshold. An MRD-negative marrow after induction is a favorable response signal; persistent MRD escalates risk and may add immunotherapy or transplant conversations. MRD does not replace the diagnostic marrow. It is a later checkpoint.

Explaining waiting for cytogenetics

Families hear a diagnosis on day 1 and then live in a gap. The honest script is: morphology and flow tell us this is leukemia, or this is a small-round-blue-cell tumor, so we can start supportive care and protocol induction. FISH may return in a few days; full karyotype and NGS often take longer. Those results may add imatinib for BCR-ABL1, change Burkitt versus lymphoblastic intensity, or move neuroblastoma risk. Waiting is not a sign the team is unsure the child has cancer. It is the difference between starting safely and locking the final roadmap. Write down what is pending. Offer to repeat the explanation. Do not invent a percentage survival from a result that is not back.

A 6-year-old starts ALL induction on Friday. Monday the parent asks why genetics are still open. You show the TLS labs that are already driving hydration, the CNS LP result that already drove IT methotrexate, and the cytogenetic board that will decide whether a TKI is added. That is diagnostic nursing.