How can you detect micro metastases in lymph nodes in patients with Ductal Carcinoma In Situ (DCIS)?

Detection of Micrometastases in Lymph Nodes in DCIS

Sentinel lymph node biopsy (SLNB) is not routinely indicated for patients with pure DCIS, as micrometastases are rare (0.9-1.5%) and primarily occur only when there is undetected invasive disease. 1

Understanding DCIS and Lymph Node Involvement

DCIS, by definition, is characterized by proliferation of ductal epithelium without penetration through the basement membrane. Pure DCIS without coexisting invasive cancer cannot invade lymphatics and spread to regional nodes. 1 However, micrometastases may be detected in some cases due to:

1. Unrecognized invasive components: Up to 20% of patients diagnosed with DCIS through image-guided breast biopsy will have invasive carcinoma identified when the entire lesion is removed 1

2. Sampling error: Core needle biopsies may miss small areas of invasion in large DCIS lesions

Detection Methods for Micrometastases

When SLNB is performed for DCIS, micrometastases can be detected through:

1. Serial sectioning: Complete examination of sentinel nodes with serial sectioning (50 μm) of the entire lymph node 2

2. H&E staining: Standard staining technique for initial examination

3. Immunohistochemistry (IHC): Used in suspicious cases to detect isolated tumor cells or micrometastases (≤0.2 mm) 1, 2

However, the ASCO guidelines do not recommend routine IHC or polymerase chain reaction for sentinel lymph node evaluation, as the significance of occult micrometastases appears to be negligible. 1

When to Consider SLNB in DCIS

SLNB should be selectively performed in DCIS in the following scenarios:

1. When mastectomy is planned 1

   • Rationale: Mastectomy precludes subsequent SLNB if invasive cancer is found
   • The mapping agent can be injected around the DCIS lesion or in the periareolar region

2. When physical examination or imaging shows a mass lesion highly suggestive of invasive cancer 1

3. When the area of DCIS by imaging is large (≥5 cm) 1

4. High-grade DCIS with increased risk of harboring invasive components 3

Risk Factors for SLN Metastases in DCIS

Factors associated with higher likelihood of SLN metastases include:

• Large tumor size (>30 mm) 2, 3
• High histological grade 2, 3
• Palpable tumor or mammographic mass 3
• Smaller core needle size used for diagnosis 4
• Comedo-type DCIS 5

Approach to Lymph Node Assessment in DCIS

For patients with DCIS undergoing breast-conserving surgery:

• SLNB can be safely omitted 4
• If invasive cancer is subsequently found, SLNB can be performed as a second procedure 1, 4

For patients with DCIS undergoing mastectomy:

• Consider SLNB at the time of mastectomy 1
• This is especially important if immediate reconstruction is planned 1

Clinical Implications of Micrometastases in DCIS

The prognostic significance of micrometastases in DCIS remains uncertain:

• Long-term survival rates of 97-99% for DCIS patients treated by surgery alone are not compatible with a significant incidence of axillary nodal metastases 1
• Most positive SLNs in DCIS are micrometastases or isolated tumor cells ≤0.2 mm 1
• When micrometastases are found, complete axillary dissection may not be necessary 5

Pitfalls to Avoid

1. Overtreatment: Performing SLNB in all DCIS cases leads to unnecessary procedures and potential complications including lymphedema 1

2. Undertreatment: Failing to perform SLNB in high-risk DCIS cases (large, high-grade, or requiring mastectomy) may necessitate a second surgery if invasive disease is found

3. Reliance on frozen section: Frozen section examination of image-guided needle biopsies for DCIS is strongly discouraged as it may miss microinvasion or render small foci uninterpretable 1

4. Overinterpretation: Not all micrometastases detected by IHC have clinical significance, and their presence should be interpreted cautiously 1