Why LCIS is Considered a Risk Marker Rather Than a Malignant Lesion
LCIS is fundamentally different from DCIS because it functions as a marker of increased bilateral breast cancer risk rather than a true premalignant lesion requiring surgical excision. 1
Key Biological and Clinical Distinctions
Bilateral and Non-Site-Specific Risk Pattern
The increased cancer risk from LCIS applies equally to both breasts, regardless of which breast contains the diagnosed focus. 1 This bilateral risk distribution is fundamentally incompatible with LCIS being a direct precursor lesion.
When invasive cancers develop after LCIS diagnosis, they occur with equal frequency in the contralateral breast as in the ipsilateral breast containing the original LCIS. 2, 3 This contrasts sharply with DCIS, where recurrences occur predominantly at the original site.
Subsequent invasive cancers are more commonly ductal rather than lobular histology. 2, 3 If LCIS were a true precursor, one would expect subsequent cancers to be predominantly invasive lobular carcinoma at the same site.
Magnitude and Timeline of Risk
LCIS confers a lifetime risk of 10-20% for subsequent breast cancer development over the next 15 years. 1, 4 This represents an 8- to 12-fold increased relative risk compared to the general population. 2, 5
Most subsequent malignancies occur more than 15 years after LCIS diagnosis, indicating an indolent natural history inconsistent with direct malignant progression. 2
Population-based data demonstrate 10-year and 20-year cumulative incidence of subsequent breast malignancy of 11.3% and 19.8% respectively. 6
Pathologic Characteristics Supporting Risk Marker Status
LCIS cells are typically of low histologic and nuclear grade, highly estrogen receptor positive, with tumor marker characteristics suggesting indolent growth and good prognosis. 2 These features differ markedly from the more aggressive cytologic and biologic characteristics of DCIS.
LCIS is assumed to be widely disseminated throughout all breast tissue when found, with close to 100% incidence of multicentricity and bilaterality. 2 This diffuse distribution pattern supports its role as a field effect marker rather than a focal premalignant lesion.
The lobular architecture and basement membrane remain intact with no evidence of stromal invasion. 2
Clinical Management Implications
Surgical Margins Are Irrelevant
The relationship between LCIS and surgical margins is not important and does not require documentation or re-excision. 1 This stands in stark contrast to DCIS, where margin assessment is arguably the most important pathologic feature.
There is no role for excision of biopsy sites to obtain clear margins. 2
Excellent Long-Term Outcomes
When subsequent breast cancers develop in women with LCIS, they are typically diagnosed at early stages with very low mortality, likely due to strict mammographic surveillance. 2
The 10-year and 20-year breast cancer-specific survival for women with LCIS is 98.9% and 96.3% respectively. 6
Most subsequent breast cancers are low/intermediate grade, hormone receptor-positive, and diagnosed in early stages. 6
Management Strategy
LCIS is managed by careful non-operative observation, similar to other risk factors such as family history or atypical hyperplasia. 2, 3
Annual mammography and clinical breast examination every 6-12 months are recommended. 1
Tamoxifen provides significant risk reduction (approximately 75% reduction in invasive breast cancer occurrence) and should be strongly considered. 7, 2
Common Pitfall to Avoid
Despite current guidelines clearly establishing LCIS as a risk marker, mastectomy rates for LCIS increased by 50% from 2000 to 2009 in the United States. 8 This represents overtreatment, as the only rational surgical treatment would be bilateral mastectomy (since risk is bilateral), which appears far too aggressive given the low overall mortality risk and excellent outcomes with surveillance. 2, 6