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5 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
Lobular carcinoma in situ is not an invasive breast cancer but a marker that a woman is at higher risk of one: abnormal cells fill the milk-producing lobules without spreading. About one in five women develop breast cancer within ten years, in either breast and of any type; preventive tamoxifen cuts that to about one in fourteen, and the pleomorphic form is excised like ductal carcinoma in situ.
The WHO classification lists lobular carcinoma in situ among the lobular neoplasias, with atypical lobular hyperplasia as its lesser form and the pleomorphic and florid variants as higher-risk forms; like invasive lobular carcinoma it has lost E-cadherin (Tan 2020). In the Memorial Sloan Kettering cohort of 1,060 women with LCIS alone, 5 percent chose bilateral prophylactic mastectomy and 1,004 chose surveillance, 173 of them with chemoprevention; at a median follow-up of 81 months, 150 women developed 168 breast cancers (63 percent in the same breast, 25 percent in the other, 12 percent both), with no dominant histology (ductal carcinoma in situ 35 percent, invasive ductal 29 percent, invasive lobular 27 percent), and the ten-year cumulative risk was 7 percent with chemoprevention against 21 percent without (King 2015). Pleomorphic LCIS behaves differently: of 21 patients with pure pleomorphic LCIS on biopsy who had excision, 33.3 percent were found to have invasive carcinoma and 19 percent ductal carcinoma in situ, and the lesion was extensive or multifocal in 47.6 percent (Annals of Surgical Oncology 2015).
How it differs from its parent: it is a risk lesion and precursor rather than a cancer, is not staged, and its management is surveillance and prevention rather than treatment of a tumour, which is why it sits beside ductal carcinoma in situ under the breast cancer page.
| Setting | Approach | Guideline |
|---|---|---|
| Classic LCIS on biopsy | Surveillance and chemoprevention (tamoxifen or an aromatase inhibitor); TAM-01 tested low-dose tamoxifen in intraepithelial neoplasia. | not mapped |
| Pleomorphic or florid LCIS | Excision to clear margins because of the upgrade rate to invasive cancer or ductal carcinoma in situ. | not mapped |