A 24-year-old woman complains of intermittent fever and joint pain. She says that these symptoms have been present for the past month. Before that, she had no signs or symptoms and was completely healthy. She has also lost her appetite and some weight. A complete blood count (CBC) showed severe pancytopenia. What is the next best step in evaluating this patient?

Repeated CBCs for several weeks and reassess

An 18-month-old boy is brought to the doctor’s office for evaluation of abdominal pain. The boy looks emaciated and he is now significantly below his growth chart predicted weight. The family history is non-contributory. The vital signs are unremarkable. On physical examination, a non-tender mass is felt in the upper part of the abdomen. A magnetic resonance image (MRI) scan of his abdomen demonstrates a mass in his right adrenal gland. Biopsy of the mass demonstrates an abundance of small round blue cells. With this biopsy result, which 1 of the following findings would confirm the diagnosis?

Elevation of vanillylmandelic acid in the urine

MRI showing the intrarenal origin of the mass

Radiograph of the bone showing the presence of lytic bone lesion with periosteal reaction

A 7-year-old boy presents to his primary care physician for a general checkup. The patient has been feeling poorly for the past several weeks and has been losing weight. He states that he often feels weak and too tired to play with his friends. He is no longer interested in many recreational activities he used to be interested in. The patient's parents state that a few of their child's friends have been sick lately. His temperature is 102°F (38.9°C), blood pressure is 77/48 mmHg, pulse is 110/min, respirations are 24/min, and oxygen saturation is 98% on room air. On exam, you note a fatigued appearing child who has lost 10 pounds since his last appointment. Left upper quadrant tenderness and a mass is noted on abdominal exam. Which of the following best describes the most likely diagnosis?

Smudge cells on peripheral smear

Infection sensitive to oseltamivir

Parental mistreatment of the child

An inconsolable mother brings her 2-year-old son to the emergency room after finding a large amount of bright red blood in his diaper, an hour ago. She states that for the past week her son has been having crying fits while curling his legs towards his chest in a fetal position. His crying resolves either after vomiting or passing fecal material. Currently, the child is in no apparent distress. Physical examination with palpation in the gastric region demonstrates no acute findings. X-ray of the abdominal area demonstrates no acute findings. His current temperature is 36.5°C (97.8°F), heart rate is 93/min, blood pressure is 100/64 mm Hg, and respiratory rate is 26/min. His weight is 10.8 kg (24.0 lb), and height is 88.9 cm (35.0 in). Laboratory tests show the following: RBC count 5 million/mm3 Hematocrit 36% Hemoglobin 12 g/dL WBC count 6,000/mm3 Mean corpuscular volume 78 fL What is the most likely underlying embryological cause predisposing to this condition?

Failure of the vitelline duct to close

Failure of the vitelline duct to open

Elevated anti-mitochondrial antibodies

Problem with bilirubin conjugation

A 75-year-old man presents to the physician because of bloody urine, which has occurred several times over the past month. He has no dysuria, flank pain, nausea, or vomiting. He has no history of serious illness and takes no medications. He is a 40-pack-year smoker. The vital signs are within normal limits. Physical exam shows no abnormalities except generalized lung wheezing. The laboratory test results are as follows: Urine Blood 3+ RBC > 100/hpf WBC 1–2/hpf RBC casts Negative Bacteria Not seen Which of the following is the most appropriate diagnostic study at this time?

Computed tomography (CT) urogram

A 2-year-old boy is brought to the physician because of progressive difficulty breathing and a productive cough for the past 2 days. During the past 6 months, he has had recurrent episodes of pneumonia treated with antibiotics. He has not gained weight in this time period. His temperature is 38.5°C (101.3°F), pulse is 130/min, respirations are 18/min, and blood pressure is 100/60 mm Hg. Auscultation of the lungs shows decreased breath sounds over the right lung fields. Ocular examination shows periorbital subcutaneous bleeding and bulging of both eyes. His leukocyte count is 16,000/mm3. An x-ray of the chest shows a right-sided opacity and a collapsed right lung. An MRI of the chest shows a heterogeneous mass in the posterior mediastinum that compresses the heart and the great vessels to the left side. Further evaluation is most likely to show which of the following?

Overexpression of the N-myc oncogene

Unregulated B-cell proliferation in the mediastinum

Acid-fast bacteria on sputum microscopy

Increased lymphoblast count in the bone marrow

Autoantibodies against nicotinic acetylcholine receptors

A 5-year-old boy is brought to the pediatric clinic for evaluation of fever, pain, swelling in the left leg, and limping. Review of systems and history is otherwise unremarkable. The vital signs include: pulse 110/min, temperature 38.1°C (100.6°F), and blood pressure 100/70 mm Hg. On examination, there is a tender swelling over the lower part of his left leg. Which 1 of the following X-ray findings is most suggestive of Ewing’s sarcoma?

X-ray showing lytic bone lesion with periosteal reaction

Mixed lytic and blastic appearance in the X-ray

X-ray showing broad-based projections from the surface of the bone

X-ray showing a sharply marginated radiolucent area within the apophysis

X-ray showing deep muscle plane displacement from the metaphysis

Diagnostic approach to pediatric malignancies for USMLE Step 1: High-Yield Pediatrics Lessons

Initial Clues - Spotting the Suspects

History is Key: Unexplained & persistent symptoms are red flags.
- Bone pain (especially nocturnal), persistent headaches (worse in AM, with vomiting), limp.
- Easy bruising, recurrent infections.
Clinical Examination Findings:
- General: Pallor, petechiae, purpura (suggests bone marrow infiltration).
- Abdomen: Palpable mass (Wilms', Neuroblastoma).
- Nodes: Firm, non-tender, matted lymphadenopathy.
- Neuro: Cranial nerve palsies, ataxia.
Constitutional "B" Symptoms:
- Unexplained fever >38°C, drenching night sweats, unexplained weight loss >10% in 6 months.

⭐ Neuroblastoma can present with opsoclonus-myoclonus syndrome (“dancing eyes, dancing feet”), a paraneoplastic syndrome.

Abdominal masses in children: Wilms, neuroblastoma, lymphoma

Lab Sleuthing - Blood & Marrow

Complete Blood Count (CBC) & Peripheral Smear:
- Initial screen revealing potential cytopenias (anemia, thrombocytopenia) or leukocytosis with blasts.
Serum Tumor Markers:
- LDH & Uric Acid: ↑ in high cell turnover (leukemia, lymphoma).
- VMA/HVA (urine): ↑ in Neuroblastoma.
- AFP / β-hCG: ↑ in Germ Cell Tumors, Hepatoblastoma.
Bone Marrow Aspiration & Biopsy:
- Cornerstone for leukemia diagnosis; also used for staging lymphoma and neuroblastoma.
- A "dry tap" on aspiration suggests marrow packing (leukemia, fibrosis) or aplasia.

⭐ WHO Diagnosis: Presence of >20% blasts in bone marrow or peripheral blood confirms Acute Leukemia.

Peripheral blood smear: Lymphoblasts in ALL

Imaging - The Inner View

First-Line Imaging:
- X-ray: Initial step for bone tumors (e.g., sunburst in osteosarcoma, onion-peel in Ewing's) and chest masses.
- Ultrasound: Differentiates solid vs. cystic lesions. Primary tool for abdominal masses like Wilms' tumor and neuroblastoma.
Advanced Cross-Sectional Imaging:
- CT Scan: Details chest, abdomen, pelvis for staging lymphomas & neuroblastomas. Balance diagnostic yield with radiation risk.
- MRI: Modality of choice for CNS tumors and soft-tissue sarcomas due to superior contrast and no radiation.
Functional/Metabolic Imaging:
- FDG-PET/CT: For staging, assessing treatment response, and detecting recurrence in lymphomas & sarcomas.
- MIBG Scan: Highly specific for neuroblastoma.

⭐ MIBG (metaiodobenzylguanidine) scan is the investigation of choice for staging neuroblastoma, showing uptake in over 90% of tumors.

Pediatric Cancer Imaging: X-ray, CT, MRI, PET, MIBG

Tissue is the Issue - Biopsy & Markers

Biopsy: The Gold Standard
- Provides definitive histologic diagnosis, grading, and tissue for molecular/genetic analysis.
- Types: Excisional (small, accessible tumors), Incisional/Core Needle (large masses), Bone Marrow Aspirate & Biopsy (leukemia/lymphoma/staging).
Key Tumor Markers & Immunohistochemistry (IHC)
- Neuroblastoma: ↑ Urine VMA/HVA, serum NSE, Ferritin. IHC: Synaptophysin, Chromogranin A.
- Wilms' Tumor: IHC: WT1.
- Ewing Sarcoma: IHC: CD99, FLI1.
- Rhabdomyosarcoma: IHC: Desmin, Myogenin.
- Hepatoblastoma: ↑ AFP.
- Germ Cell Tumors: ↑ AFP, β-hCG.

⭐ Small Round Blue Cell Tumors (SRBCTs) have significant overlap. A panel of markers is crucial. Ewing Sarcoma is classically CD99 positive, while Rhabdomyosarcoma is Myogenin/Desmin positive.

Immunohistochemistry for pediatric small round cell tumors

High‑Yield Points - ⚡ Biggest Takeaways

Histopathology (HPE) & Immunohistochemistry (IHC) are the gold standard for diagnosis.

Key tumor markers: AFP (yolk sac), β-hCG (germ cell tumors), and urinary VMA/HVA (neuroblastoma).

MRI is preferred for CNS and soft tissue tumors; PET-CT is crucial for staging.

Bone marrow aspiration & biopsy are mandatory for suspected leukemia and lymphoma.

Molecular markers like N-myc amplification in neuroblastoma are critical for prognosis.

Always consider age: Neuroblastoma in infants, Wilms' tumor in toddlers, sarcomas in adolescents.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play