Lobular carcinoma in situ (LCIS) is not only a relative newcomer among
breast lesions, but in its short span of 50 years it has gradually ev
olved from a rare form of breast cancer to being merely a marker of in
creased risk. This change has not been without controversy which persi
sts to the present day, although there is now general agreement on the
natural history of the disease. The present report represents an upda
te on current thinking about LCIS as well as a review of the limited n
umber of studies dealing with the natural history of the lesion when t
reated by biopsy alone. Invasive cancer will develop in approximately
20-25% of women with LCIS provided there is sufficient follow-up after
biopsy. Precise estimates are not possible since LCIS is an asymptoma
tic lesion that never makes a mass or reveals itself on mammography. I
t is found only by biopsy and thus the population being followed is a
selected one. Every study has shown that when invasive cancer develops
, it is just as likely to appear in the contralateral as in the biopsi
ed breast, and invasive ductal cancers are more common than lobular. C
learly, the small round cells with pale cytoplasm that characterize LC
IS do not go on to invasion in the usual patient; rather they serve to
identify women who are more likely to develop breast cancer. Such pat
ients represent a clearly defined group at increased risk, and for tha
t reason are ideal candidates for chemoprevention. If tamoxifen or som
e other agent proves to be effective, the remaining arguments favoring
mastectomy for LCIS will finally disappear. (C) 1993 Wiley-Liss, Inc.