The current consensus is that LCIS should not be treated as a cancer, but rather, is a marker for increased breast cancer risk. It has been suggested that a more appropriate term for this pathologic entity may be “lobular neoplasia.” LCIS affects only women, has a peak incidence at age 45, and decreases in incidence after menopause. It has been estimated that as many as 90% of women with LCIS are premenopausal, and estrogen receptors are found in most lesions. Therefore, the development of LCIS may be related to hormonal influences.

A woman diagnosed with LCIS has a risk of developing an invasive breast cancer that is 8 to 11 times the risk of the general population. The absolute risk of invasive breast cancer development is 20% to 25% in the 15 years after the diagnosis of LCIS is made. LCIS appears to arise from the terminal duct-lobular apparatus, and the disease tends to be multifocal, multicentric, and bilateral.

Lobular carcinoma in situ is an incidental finding on microscopy without distinctive features on clinical, mammographic, or gross pathological examination. It is commonly found in multiple areas of the breast ("multicentric") and is only rarely associated with occult invasive cancers. The true incidence of lobular carcinoma in situ in the general population is unknown, since it lacks clinical or mammographic signs; most series report this finding in 1 to 3 percent of breast-biopsy specimens. It is more frequent among premenopausal women, in part because such women more commonly have the benign breast abnormalities that require biopsy. The frequency of the diagnosis appears to be increasing, with a 15 percent increase in the number of cases from 1973 to 1988 in one series.. This increase may simply be due to the increased number of breast biopsies performed.

The most important issue in the management of lobular carcinoma in situ is whether it is a premalignant lesion or a marker of increased risk for the development of breast carcinoma. Long-term follow-up of patients with lobular carcinoma in situ who were treated with biopsy alone has revealed a subsequent risk of invasive breast cancer of approximately 1 percent per year for at least 15 years, corresponding to a relative risk of approximately 7 to 10. It is noteworthy that the risk of invasive breast cancer in all these series was roughly equal for both the ipsilateral and contralateral breast and that in most cases, the subsequent cancer was invasive ductal, rather than lobular. This information supports the idea that lobular carcinoma in situ is a marker of increased risk for the development of cancer. Efforts to identify features of lobular carcinoma in situ associated with a higher likelihood of cancer have been unsuccessful; histologic features, including the extent of the lesion, are not predictive of the subsequent development of invasive carcinoma. Patients with lobular carcinoma in situ have a risk of invasive cancer approximately twice as high as that of patients with atypical lobular hyperplasia.

The chief treatment option for patients with lobular carcinoma in situ is careful observation, as would be carried out for any woman known to be at increased risk for breast cancer, such as those with a family history of breast cancer or a history of previous breast cancer. Bilateral total mastectomy (with or without reconstruction) can be considered as a prophylactic treatment in the small minority of patients who are very uncomfortable with this increased level of risk. Radiotherapy has no role in the management of lobular carcinoma in situ. It is unnecessary to identify histologically negative margins in women who elect to undergo observation, because lobular carcinoma in situ is known to be multicentric and is viewed as a marker lesion.
New England Journal of Medicine -- July 30, 1992 -- Volume 327, Number 5 

Introduction (from the NCI.

The term lobular carcinoma in situ (LCIS) is misleading. This lesion is more appropriately termed lobular neoplasia. Strictly speaking, it is not known to be a premalignant lesion, but rather a marker that identifies women at an increased risk for subsequent development of invasive breast cancer. This risk remains elevated even beyond 2 decades, and most of the subsequent cancers are ductal rather than lobular. LCIS is usually multicentric and is frequently bilateral. In a large prospective series from the National Surgical Adjuvant Breast and Bowel Project with a 5-year follow-up of 182 women with LCIS managed with excisional biopsy alone, only 8 women developed ipsilateral breast cancer (4 of them invasive). In addition, 3 developed contralateral breast tumors (2 of them invasive).

Treatment option overview

Most women with LCIS can be managed without additional local therapy after biopsy. No evidence is available that re-excision to obtain clear margins is required. Tamoxifen has decreased the risk of developing breast cancer in women with LCIS and should be considered in the routine management of these women. The Breast Cancer Prevention P-1 trial of 13,388 high-risk women comparing tamoxifen to placebo demonstrated an overall 49% decrease in invasive breast cancer, with a mean follow-up of 47.7 months. Risk was reduced by 56% in the subset of 826 women with a history of LCIS, and the average annual hazard rate for invasive cancer fell from 12.99 per 1,000 women to 5.69 per 1,000 women. In women older than 50 years, this benefit was accompanied by an annual incidence of 1 to 2 per 1,000 women of endometrial cancer and thrombotic events. (Refer to the PDQ summary on Prevention of Breast Cancer for a detailed discussion of the risks and benefits of tamoxifen in a prevention setting.) Bilateral prophylactic mastectomy is sometimes considered an alternative approach for women at high risk for breast cancer. Many breast surgeons, however, now consider this to be an overly aggressive approach. Axillary lymph node dissection is not necessary in the management of LCIS.

Treatment options for patients with LCIS

1. Observation after diagnostic biopsy.
2. Tamoxifen to decrease the incidence of subsequent breast cancers.
3. Ongoing breast cancer prevention trials.