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, nodal (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.
4. Cancer within adipose tissue may be classified as a lymph node metastasis.
   • In the context of breast cancer: breast cancer in axillary adipose tissue in the absence of normal breast tissue, absence of in situ breast carcinoma and absence of residual lymphoid tissue is classified as a lymph node metastasis/micrometastasis/isolated tumour cells in lymph node.

DDx - mimics of metastatic disease:

• Endometriosis.
• Ectopic decidua.
• Endosalpingiosis.
• Nodal (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.
  • In the head & neck they are generally considered tumour replaced lymph nodes - though this appears to be evolving.
  • In the colon and rectum tumour deposits are considered separately and not counted as lymph nodes.
• Benign thyroid inclusion - somewhat controversial, see aberrant thyroid tissue.

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 change 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.).

Counting lymph nodes

The number of lymph nodes is usually based on:

1. Number of possible lymph nodes at the time of gross or cut-up.
2. Number of tissue fragments with definite lymph node.
   • Lymph node = lymphoid tissue + capsule.
3. Whether tumour nodules without lymphoid tissue are classified as lymph nodes or tumour deposits - dependent somewhat on the anatomical site.

Notes:

• Generally, the number of lymph nodes in a block should not exceed the number of possible lymph nodes seen at gross.

Sign out

Lymph Nodes, Left Axilla, Radical Lymph Node Dissection:
     - Three lymph nodes with METASTATIC MALIGNANT MELANOMA 
        of twenty lymph nodes (3/20).
     -- Largest focus of melanoma: 2.1 cm.
     -- Extranodal extension: ABSENT.
     - Benign skin.

Matted lymph nodes - comment

Comment:
The size of the largest lymph node metastasis is indeterminate, as the large tumour mass (6.5 cm maximal dimension) consists of matted nodes. Clinical and radiologic correlation is suggested.

See also

• Lymph node pathology.
• Cancer.
• Cancer staging.
• Lateral aberrant thyroid tissue.
• Sentinel lymph node.
• Extranodal extension.