Lymph node metastasis

Lymph node metastasis
Diagnosis in short
Lymph node metastasis (colorectal carcinoma). H&E stain.
LM	malignant cells foreign to the lymph node - typically subcapsular sinus; morphology dependent on specific cancer
Subtypes	dependent on primary tumour - macrometastasis, micrometastasis, isolated tumour cells
LM DDx	endometriosis, ectopic decidua, endosalpingiosis, melanocytic nevus, dermatopathic lymphadenopathy, sinus histiocytosis, tumour deposit (dependent on site), pathology of the lymph node - see lymph node pathology and lymphoma
Stains	dependent on tumour
IHC	dependent on tumour
Gross	enlarged lymph node, esp. spherical, white mass with an irregular border +/-extension into surround adipose tissue
Site	lymph node - see lymph node pathology
Clinical history	+/-suspicion of cancer
Signs	+/-large lymph node/mass
Prevalence	common - esp. in advanced cancer
Prognosis	dependent on specific type of cancer, +/-number of nodes affected
Clin. DDx	reactive lymphadenopathy, lymphoma, other benign causes of lymphadenopathy - see lymph node pathology
Treatment	dependent on underlying cancer (type and stage)

Lymph node metastasis is cancer that has spread to a lymph node.

General

• Determination of lymph node status is one of the most common indications for the examination of lymph nodes.
• It is a good idea to look at the tumour (if available) ...before looking at the LNs for mets.
• Lymph node metastasis, in the absence of other metastases, often up-stage a cancer from stage II to stage III.

Gross

• Outside/surface of lymph node:
  • "Large" - size varies by site.‡
    • Neck >10 mm.
  • Shape - round more suspicious than oval.
• Sectioned lymph node:
  • White firm lesion with irregular border - classic appearance.
  • Non-fatty hilum.

Note:

• ‡ Small lymph nodes (<3 mm) infrequently affect the stage - at least in colorectal adenocarcinoma.

Microscopic

Features:

• Foreign cell population - key feature.
  • Classic location: subcapsular sinuses.
• +/-Cells with cytologic features of malignancy.
  • Nuclear pleomorphism (variation in size, shape and staining).
  • Nuclear atypia:
    • Nuclear enlargement.
    • Irregular nuclear membrane.
    • Irregular chromatin pattern, esp. asymmetry.
    • Large or irregular nucleolus.
  • Abundant mitotic figures.
• +/-Cells in architectural arrangements seen in malignancy; highly variable - dependent on tumour type and differentiation.
  • +/-Gland formation.
  • +/-Single cells.
  • +/-Small clusters of cells.

Notes:

1. Cytologic features of malignancy may not be present; some tumours, e.g. gallbladder carcinoma, do not always have overt cytologic features of malignancy.
   • The diagnosis is based on the fact that they are foreign to the lymph node and architecturally consistent with a well-differentiated malignancy.
2. Lymph node metastases in sarcomas are uncommon; they are seen in <3% of cases.
3. Fatty lymph nodes (esp. fatty hilus) are less likely to harbor metastases.

DDx - mimics of metastatic disease:

• Endometriosis.
• Ectopic decidua.
• Endosalpingiosis.
• Melanocytic nevus - intracapsular or within the trabeculae.
  • Incidence estimated at ~ 0.5% in axillary lymph nodes.
• Dermatopathic lymphadenopathy.^{[citation needed]}
• Sinus histiocytosis - especially for the junior resident.
• Tumour deposit (discoutinuous extramural extension) - definition dependent on primary tumour (e.g. in the head & neck they are tumour replaced lymph nodes, in the colon they are considered separate and not counted as lymph nodes).

Images

• 

  Breast carcinoma LN metastasis (WC)

• 

  Thyroid carcinoma LN metastasis (WC)

• 

  Colorectal carcinoma LN metastasis (WC)

• 

  Melanoma in a lymph node. (WC)

Mimics

• 

  Decidua in a LN - low mag. (WC)

• 

  Decidua in a LN - high mag. (WC)

• 

  Endometriosis in a LN - intermed. mag. (WC)

• 

  Endosalpingiosis in a LN - intermed. mag. (WC)

• 

  Endosalpingiosis in a LN - very high mag. (WC)

Staging

It is customary to record:

1. The size of the largest lymph node metastasis.‡
   • It is a dictum of the Association of Directors of Anatomic and Surgical pathology that masses >3 cm are matted lymph nodes/confluent lymph nodes or a tumour mass.
2. The presence/absence of extranodal extension.
   • Tumour grows into the surrounding fat or extends beyond the contour of the lymph node in association with desmoplasia.

Note:

• ‡ Large size is considered significant at some anatomical sites, e.g. pharynx. It may changes the N stage.

Number of lymph nodes

• The number of lymph nodes is important for staging, as a small number may lead to stage migration (Will Rogers phenomenon); thus, the number of lymph nodes is often used as a quality measure.

Selected cancers and standard (minimum number of lymph nodes):

• Stomach cancer - 16 lymph nodes.
• Colorectal cancer - 12 lymph nodes.
• Esophageal cancer - no minimum as per UICC/AJCC staging - based on Li et al. - several studies give different numbers (18 lymph nodes Greenstein et al., 23 lymph nodes Peyre et al.).

See also

• Lymph node pathology.
• Cancer.
• Cancer staging.