Table 1

Summary of AJCC (8th edition) TNM staging for MCC

StagePrimary tumor (T)Lymph node (N)Metastasis (M)
0In situ primary tumorNo regional lymph node metastasisNo distant metastasis
I (clinical)Tumor ≤2 cm acrossNo lymph node metastasis (clinical exam)No distant metastasis
I (pathological)Tumor ≤2 cm acrossNo lymph node metastasis (pathological exam)No distant metastasis
IIA (clinical)Tumor >2 cm acrossNo lymph node metastasis (clinical exam)No distant metastasis
IIA (pathological)Tumor >2 cm acrossNo lymph node metastasis (pathological exam)No distant metastasis
IIB (clinical)Tumor has invaded bone, muscle, fascia, or cartilageNo lymph node metastasis (clinical exam)No distant metastasis
IIB (pathological)Tumor has invaded bone, muscle, fascia, or cartilageNo lymph node metastasis (pathological exam)No distant metastasis
III (clinical)Any tumor size or depthAt least one lymph node positive (clinical exam)No distant metastasis
IIIA (pathological)Any tumor size or depthAt least one lymph node positive (pathological exam only, not apparent through clinical exam)No distant metastasis
Primary tumor not detectedAt least one lymph node positive (clinical and pathological exam)No distant metastasis
IIIB (pathological)Any tumor size or depthAt least one lymph node positive (clinical and pathological exam) or in-transit metastasis*No distant metastasis
IV (clinical)Any tumor size or depth or no primary tumor detectedRegional lymph node may or may not be positiveDistant metastasis (clinical exam)
IV (pathological)Any tumor size or depth or no primary tumor detectedRegional lymph node may or may not be positiveDistant metastasis (pathological exam)
  • A clinical exam for nodal or metastatic disease may involve physical inspection, palpation, and/or imaging. Clinical stages assume no pathological exam has been performed. A pathological exam for nodal disease may involve sentinel lymph node biopsy, lymphadenectomy, or fine-needle biopsy. A pathological exam for metastatic disease may involve biopsy of the metastatic lesion.

  • *Located between the primary tumor and draining regional lymph nodes or distal to the primary tumor.

  • AJCC, American Joint Committee on Cancer; M, metastasis; MCC, Merkel cell carcinoma; N, lymph node; T, primary tumor; TNM, tumor, node, metastasis.