Background. Infiltrating lobular carcinomas (ILC) represent approximat
ely 10% of all breast cancers. The literature is mixed regarding their
prognosis when compared with infiltrating duct carcinomas (IDC). Ther
e are few data regarding the treatment of ILC with radiation therapy.
Methods. The clinical, pathologic, laboratory, and survival data of 16
1 patients with ILC were compared with the data of 1138 patients with
IDC. Results. ILCs were larger, more difficult to excise completely, a
nd more difficult to diagnose clinically. All prognostic factors measu
red were more favorable for ILC. Nodal positivity for ILC was 32%, com
pared with 31% for IDC (P = 0.221. The 7-year disease-free Kaplan-Meie
r survival (DFS) was 74% for patients with ILC and 63% for patients wi
th IDC (P < 0.03). The 7-year breast cancer specific survival (BCSS) w
as 83% for patients with ILC and 77% for patients with IDC (P < 0.04).
Selected patients with smaller lesions were treated with excision and
radiation therapy. Patients with ILC treated with radiation therapy h
ad a better DFS and BCSS than did patients with IDC treated with radia
tion therapy. Conclusions. ILCs often are homogeneous, small cell tumo
rs of low nuclear grade. Their desmoplastic reaction may be absent or
less marked than that of IDC, making them more difficult to palpate an
d to visualize mammographically. Despite this, they can be treated suc
cessfully with either mastectomy or excision and radiation therapy.