Microinvasion with DCIS – How Common is it? – Rodrigo Arrangoiz MS, MD, FACS, FSSO

Ductal carcinoma in situ (DCIS):
- Is, by definition, a non-invasive breast malignancy confined to the ductal system:
  - But in a meaningful minority of cases, pathologists identify a tiny focus of invasion measuring 1 mm or less—so-called DCIS with microinvasion (DCISM)
- How often does this actually happen?
  - The answer depends on how you frame the question.
The Short Answer:
- Microinvasion is identified in roughly:
  - 5% to 10% of all DCIS cases
- DCIS with microinvasion:
  - Accounts for about 1% to 2% of all breast cancers (Sopik et al., Breast Cancer Research and Treatment, 2018; Zheng et al., Journal of International Medical Research, 2020)
The reported rate varies widely, however, and two very different clinical questions often get lumped together:
- What proportion of diagnosed DCIS turns out to contain a microinvasive focus?
- How often does a core-biopsy diagnosis of DCIS get upstaged at surgical excision?
Microinvasion Within Diagnosed DCIS:
- In large surgical and pathologic series:
  - The numbers cluster at the lower end of the 5% to 10% range:
    - The UK Sloane Project (n = 11,285) recorded microinvasion in 4.6% of DCIS patients:
      - Though individual screening units reported rates anywhere from 0% to 25% (Shaaban et al., British Journal of Cancer, 2022)
    - A single-center series of 148 surgically treated DCIS cases:
      - Found microinvasive foci in 14.9% (Scheidegger et al., Human Pathology, 2025)
    - The spread largely reflects differences in how aggressively specimens are sectioned and sampled

Upstaging From Core Biopsy:
- Because core-needle biopsy samples only a fraction of the lesion:
  - DCIS diagnosed on core biopsy is frequently “upstaged” once the whole specimen is examined:
    - Approximately 6.6% of core-biopsy DCIS is upstaged to microinvasive disease, and around 22% to frank invasive carcinoma:
      - With an overall upstaging range of 8% to 47% across studies (Walters et al., Histopathology, 2015).
- A meta-analysis cited by the American College of Radiology:
  - Reported an overall DCIS-to-invasive upstaging rate of 25.9% (Kuzmiak et al., Journal of the American College of Radiology, 2025)
- When the core biopsy already shows microinvasion:
  - Upstaging to measurable invasive cancer (> 1 mm) occurs in about 28% to 37%:
    - Yet nodal positivity remains low (~1% to 7%) (Phantana-Angkool et al., Annals of Surgical Oncology, 2019)
What Predicts Microinvasion?
- Microinvasion is consistently linked to:
  - Higher-risk DCIS features
- Independent predictors in the Sloane Project and other series include:
  - High nuclear grade
  - Large DCIS extent (≥ 2.6 cm)
  - Comedo necrosis
  - Solid / cribriform architecture
  - PR negativity (Shaaban et al., British Journal of Cancer, 2022; de Mascarel et al., Cancer, 2002)
Why It Matters Clinically:
- Despite the “invasive” label, microinvasive disease carries a low nodal metastasis rate (roughly 2% to 6%, range 0% to 20%) and a generally favorable prognosis (Sopik et al., Breast Cancer Research and Treatment, 2018):
  - For this reason, management largely follows DCIS principles:
    - Including the DCIS margin standard of > 2 mm
- That said, the Sloane Project offered an important caveat:
  - Compared with pure DCIS, microinvasive disease was associated with:
    - Higher distant metastasis (1.2% vs 0.3%) and higher breast cancer mortality (2.1% vs 0.8%):
      - Suggesting more aggressive biology in a subset of patients (Shaaban et al., British Journal of Cancer, 2022)
The Takeaway for Readers:
- “Incidence of microinvasion in DCIS” is best answered with a range—about 5% to 10% of diagnosed DCIS:
  - Nearer 5% in rigorously standardized series, while keeping the separate upstaging question in mind when counseling patients after a core-biopsy diagnosis