TNM Staging of Testicular Germ Cell Tumors
The TNM staging system for testicular germ cell tumors uses pathological assessment of the primary tumor (pT), clinical and pathological assessment of regional lymph nodes (N/pN), distant metastasis (M), and uniquely incorporates serum tumor markers (S) as a formal staging parameter. 1
Primary Tumor (pT) Classification
The pT staging is determined from the radical orchiectomy specimen:
- pTis: Germ cell neoplasia in situ (GCNIS) - formerly called carcinoma in situ
- pT1: Tumor limited to testis and epididymis without vascular/lymphatic invasion; may invade tunica albuginea but not tunica vaginalis
- pT2: Tumor limited to testis and epididymis with vascular/lymphatic invasion, OR tumor extending through tunica albuginea with involvement of tunica vaginalis
- pT3: Tumor invades spermatic cord (with or without vascular/lymphatic invasion)
- pT4: Tumor invades scrotum (with or without vascular/lymphatic invasion) 1
Critical distinction: The presence or absence of vascular/lymphatic invasion is the key differentiator between pT1 and pT2 when the tumor is confined to the testis and epididymis. The AJCC 8th edition further subdivides T1 pure seminoma into T1a (≤3 cm) and T1b (>3 cm). 1
Regional Lymph Nodes
Clinical Stage (N):
- N0: No regional lymph node metastasis
- N1: Lymph node mass ≤2 cm in greatest dimension, OR multiple nodes none >2 cm
- N2: Lymph node mass >2 cm but ≤5 cm, OR >5 nodes positive (none >5 cm), OR extranodal extension
- N3: Lymph node mass >5 cm 1
Pathological Stage (pN):
- pN1: Lymph node mass ≤2 cm AND ≤5 positive nodes (none >2 cm)
- pN2: Lymph node mass >2 cm but ≤5 cm, OR >5 nodes positive (none >5 cm), OR extranodal extension
- pN3: Lymph node mass >5 cm 1
Key difference: Pathological staging adds the requirement of ≤5 positive nodes for pN1, whereas clinical N1 has no such numerical limit.
Distant Metastasis (M)
- M0: No distant metastasis
- M1a: Non-regional lymph node(s) or lung metastasis
- M1b: Distant metastasis other than non-regional lymph nodes and lung (e.g., bone, liver, brain) 1
Serum Tumor Markers (S)
This is unique to testicular cancer staging - serum markers are formally incorporated into the TNM system and measured pre-chemotherapy:
- S0: Marker levels within normal limits
- S1: LDH <1.5× ULN AND hCG <5,000 mIU/mL AND AFP <1,000 ng/mL
- S2: LDH 1.5-10× ULN OR hCG 5,000-50,000 mIU/mL OR AFP 1,000-10,000 ng/mL
- S3: LDH >10× ULN OR hCG >50,000 mIU/mL OR AFP >10,000 ng/mL 1
Critical Staging Considerations
Timing of assessment matters: Histopathological results, post-orchiectomy tumor markers, and contrast-enhanced CT scan results are used together to stratify patients according to TNM classification. 1
Seminoma-specific caveat: In patients with pure seminoma and serum β-hCG >1,000 IU/L, consider the possibility of nonseminoma, re-review the surgical specimen with pathology, and consider discussion with a high-volume center. β-hCG alone should not be used to stage or risk stratify patients with pure seminoma. Use of LDH to risk stratify metastatic seminoma is controversial. 2
Elevated AFP in "seminoma": Patients with elevated AFP have nonseminomas by definition, regardless of histology. 2
Stage Grouping Integration
The final stage grouping (Stage 0, I, IA, IB, IS, II, IIA, IIB, IIC, III, IIIA, IIIB, IIIC) combines T, N, M, and S categories with histology (seminoma vs. nonseminoma) to determine prognosis and guide treatment decisions. 1 This integrated approach is essential because serum markers provide independent prognostic information beyond anatomical extent of disease alone.