LOBULAR NEOPLASIA

• Lobular carcinoma in situ (LCIS) was first described by:
  • Foote and Stewart in 1941
• The term ‘‘lobular neoplasia,’’ encompassing both atypical lobular hyperplasia (ALH) and LCIS:
  • Was later coined in 1978 by Haagensen et al
• Both ALH and LCIS are composed of an:
  • Atypical monomorphic epithelial proliferation:
    • Arising within the terminal ductal lobular unit
  • Characteristically, the atypical cells are:
    • Small and dyshesive:
      • Often have intracytoplasmic vacuoles
  • In both ALH and classic LCIS, the atypical cells:
    • Fill and distend the acini:
      • At times, the ducts within one or more terminal ductal lobular unit
• The pathologic distinction between ALH and classic LCIS is made:
  • Primarily on the quantity of atypia:
    • Lobular carcinoma in situ is defined as:
      • The filling and distension of more than 50% of the acini in a terminal ductal lobular unit
      • Whereas ALH is used to denote lesions that fail to meet this criterion
• Lobular neoplasia:
  • Is associated with increased relative risk of carcinoma development including both ductal carcinoma in situ (DCIS) and invasive cancer:
    • 8- or 9-fold increased risk for LCIS
    • 4- or 5-fold increased risk for ALH:
      • In either breast
  • Recent estimates of absolute risk suggest:
    • 1% to 2% per year for ALH
    • 2% per year for LCIS
• Usually, ALH is an incidental finding identified on a CNB performed for another reason:
  • Is identified in less than 1% of CNBs performed
• Similarly, LCIS is identified in:
  • Approximately 1% of CNBs performed after screening mammography
• Initial reports on rates for upgrade of lobular neoplasia on CNB to invasive cancer or DCIS at surgical excision:
  • Ranged from 0% to 50%:
    • However, many earlier studies lacked radiologic-pathologic correlation to exclude discordant cases, and often ALH and LCIS cases were not differentiated
• A few recent studies have provided increased clarity on upgrade risk for ALH and LCIS diagnosed by CNB:
  • In a large retrospective review of 32,960 breast core biopsies by Chang Sen et al:
    • 13 447 were found to have ALH or classic LCIS with no other associated high-risk lesions:
      • Among the 447 lesions:
        • 22 (4.9%) were malignant at excision:
          • 10 cases of invasive cancer and 12 cases of DCIS
      • The upgrade rate was:
        • 8.4% for LCIS
        • 2.4% for ALH
          • The authors concluded that surveillance at 6, 12, and 24 months could be performed in lieu of excision for ALH:
            • After biopsy of calcifications, that are well sampled with concordant benign results
            • Excision still was recommended for LCIS
• These findings are further supported by a prospective study of 79 patients with a CNB diagnosis of pure lobular neoplasia:
  • In this study, the upgrade rate was 3% by local pathology and 1% by central pathology review:
    • Demonstrating that routine excision is not indicated for patients with pure lobular neoplasia on CNB and concordant imaging findings
• Furthermore, studies reporting on ALH and LCIS diagnosed on CNB with clinical radiologic follow-up evaluation:
  • Indicate that the likelihood of carcinoma developing at the core biopsy site within 3 to 5 years (some of which may represent carcinoma missed at the time of the original CNB):
    • Is 2% or less:
      • Thus, for incidental lobular neoplasia (either ALH or classic LCIS) on CNB in cases that lack other indications for excision and with radiologic-pathologic concordance:
        • Observation may be appropriate

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