- When to omit SLNB (new, practice-changing):
- ASCO now recommends not performing routine SLNB in a clearly defined low-risk subgroup if omitting nodal pathology will not change adjuvant plans:
- Postmenopausal:
- ≥ 50 years
- HR-positive / HER2-negative
- Grade 1 to 2
- Tumor ≤ 2 cm (cT1)
- Pre-op axillary ultrasound negative
- Breast-conserving therapy planned
- Team agrees systemic therapy and RT will not be altered by SLNB findings:
- Postmenopausal:
- Recommendation built on SOUND and INSEMA randomized trials:
- Observed outcomes in the RCTs:
- Omission was non-inferior to SLNB for iDFS / distant DFS
- Regional events were rare
- Arm morbidity lower without surgery
- Observed outcomes in the RCTs:
- ASCO also emphasizes:
- Do not escalate or alter adjuvant systemic therapy or radiation just because SLNB was omitted:
- Plan treatments as you would for this low-risk profile
- Do not escalate or alter adjuvant systemic therapy or radiation just because SLNB was omitted:
- ASCO now recommends not performing routine SLNB in a clearly defined low-risk subgroup if omitting nodal pathology will not change adjuvant plans:
- When SLNB is still appropriate:
- Outside the narrow “omit” criteria above:
- >2 cm
- High-grade
- TNBC
- HER2+
- Multifocality affecting RT fields
- No reliable AUS
- Planned mastectomy where nodal information might change PMRT
- After neoadjuvant therapy:
- Initially cN0 or cN1→cN0:
- ASCO continues to support SLNB (or targeted axillary dissection when appropriate) to document response:
- The 2025 update centers on upfront surgery, don’t generalize omission to neoadjuvant settings
- ASCO continues to support SLNB (or targeted axillary dissection when appropriate) to document response:
- Initially cN0 or cN1→cN0:
- Outside the narrow “omit” criteria above:
- When to omit completion ALND:
- 1 to 2 positive sentinel nodes after upfront surgery:
- Continue to omit ALND with whole-breast RT (Z0011 / AMAROS era practice remains)
- After mastectomy with 1 to 2 positive SNs and delivery of PMRT to chest wall + regional nodes:
- ASCO supports omitting ALND (supported by SENOMAC data):
- Coordinate fields with radiation oncology
- ASCO supports omitting ALND (supported by SENOMAC data):
- 1 to 2 positive sentinel nodes after upfront surgery:
- Radiation interface (2025 ASTRO / ASCO / SSO PMRT update):
- Joint 2025 PMRT guideline clarifies when PMRT / regional nodal irradiation is indicated and explicitly supports ALND omission if PMRT is given for 1 to 2 positive SNs post-mastectomy
- Use multidisciplinary planning to balance coverage / toxicity when nodal pathology is limited or absent
- Practical checklist for your clinic (BCT, upfront surgery):
- AUS first:
- If AUS negative and patient fits the low-risk profile above → discuss no SLNB
- Document that omission won’t change systemic / RT plans
- If AUS suspicious → needle sample:
- Positive = manage per current standards:
- SLNB ± targeted node or ALND / RT depending on context
- If SLNB done and 1 to 2 SN+ → omit ALND:
- Ensure appropriate RT fields (BCT) or PMRT (after mastectomy)
- Positive = manage per current standards:
- Neoadjuvant cases:
- Do not translate “omit SLNB” from SOUND / INSEMA:
- Use SLNB / TAD pathways
- Do not translate “omit SLNB” from SOUND / INSEMA:
- AUS first:
- Pearls and Pitfalls:
- Selection discipline matters:
- The non-inferiority signal depends on accurate AUS triage and truly low-risk biology
- Don’t “compensate” with extra RT or chemotherapy solely because you omitted SLNB:
- ASCO warns against reflex escalation
- Documentation:
- Note eligibility criteria, shared decision discussion, and that omission won’t impact adjuvant choices
- Monitor the edge cases (young age, lobular histology, multifocality):
- Trials had limited power there:
- Consider SLNB if nodal information could change RT / systemic therapy
- Trials had limited power there:
- Selection discipline matters:
- Sources / key reads:
- ASCO Guideline Update (2025) — SLNB in early breast cancer; ASCO Post summary with criteria and implementation notes.
- INSEMA (NEJM 2025) — Omission of axillary surgery vs SLNB; non-inferior iDFS, less morbidity.
- SOUND (JAMA Oncol 2023) — No axillary surgery vs SLNB in small tumors with negative AUS; non-inferior distant DFS.
- PMRT 2025 Joint Guideline (ASTRO/ASCO/SSO) — When to deliver PMRT and how it enables ALND omission with limited SN positivity after mastectomy.
Rodrigo Arrangoiz MS, MD, FACS, FSSO 