Microinvasion in Ductal Carcinoma In Situ (DCIS)

• The eighth edition of the American Joint Committee on Cancer (AJCC) staging system:
  • Defines microinvasion as:
    • Invasion of breast cancer cells through the basement membrane at one or more foci:
      • None of which exceeds a dimension of 1 mm
  • DCIS:
    • Is a T0 lesion:
      • Is classified as stage 0 cancer
  • DCIS with microinvasion is considered:
    • T1mi:
      • Upstages DCIS from stage 0 to stage I disease:
        • The earliest stage of invasive cancer:
          • In the AJCC staging system
• By definition:
  • DCIS does not have the ability to metastasize to axillary lymph nodes or distant sites:
    • Whereas DCIS with microinvasion does
• Axillary metastasis:
  • Has been reported in 0% to 20% of patients:
    • With DCIS with microinvasion
• The incidence of microinvasion in DCIS:
  • Varies according to the size and extent of the index lesion
  • Lagios et al. (1989):
    • Reported a 2% incidence of microinvasion in patients with DCIS:
      • Measuring less than 25 mm in diameter
    • Compared with a 29% incidence of microinvasion:
      • In those with lesions larger than 26 mm
  • The incidence of microinvasion is also higher in patients with:
    • High-grade or comedo-type DCIS with necrosis
    • In patients with DCIS who present with:
      • A palpable mass
      • Nipple discharge
• Historically, patients with DCIS with microinvasion:
  • Have been observed to have a worse prognosis compared with those who have DCIS alone
  • Mirza et al. (2000):
    • Reported the long-term results of breast-conserving therapy in patients with:
      • DCIS
      • DCIS with microinvasion
      • T1 invasive breast cancers
    • The 20-year disease-specific survival rates in patients with:
      • DCIS were better:
        • Than those among patients with DCIS with microinvasion or with T1 invasive tumors
      • Patients with microinvasion and those with T1 tumors:
        • Had similar survival rates
  • In a retrospective study of 1,248 serially sectioned DCIS tumors, de Mascarel et al. (2002):
    • Reported a 10.1% incidence of axillary metastases in cases of DCIS with microinvasion
    • Patients with DCIS had a better 10-year distant metastasis-free survival rate:
      • Than patients with DCIS with microinvasion:
        • 98% and 91%, respectively
    • The overall survival rate was also better in patients with DCIS:
      • 96.5% vs. 88.4%
    • However, the metastasis-free and overall survival rates:
      • Were worse in patients with invasive ductal carcinoma compared with those with DCIS with microinvasion
    • These results suggest that DCIS with microinvasion:
      • Should be characterized as a small invasive tumor with a good outcome and that the therapeutic approach for these patients should be similar to that for patients with invasive cancer
• However, more recent studies have pointed toward DCIS with microinvasion having a more similar natural history to pure DCIS than to early-stage invasive disease:
  • In a review of 393 patients treated at Yale between 1973 and 2004:
    • There was no statistically significant difference between patients with DCIS and those with DCIS with microinvasion with regard to the presence of axillary metastases (in those who had axillary staging) or the likelihood of recurrence (locoregional and distant) or overall survival (Parikh et al., 2012)

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