Background: Interstitial laser therapy (ILT) is a technique of destroying tumor cells via thermal energy. Prior studies have shown that the procedure is safe and efficacious in laboratory animals and that complete cell death, as assessed by tetrazollium staining, is achieved in the laser treated area.

Design: Forty women with localized, mammographically detectable, T1 breast cancers consented to be treated with ILT and then have the treated area subsequently excised. The delay period ranged from 5 to 42 days. Prior to ILT, the diagnosis of breast carcinoma was established by stereotactic needle core biopsy.

Results: All 40 cases showed a characteristic gross appearance, which consisted of a series of concentric rings surrounding a cavity corresponding to the laser needle tip. The tissue immediately adjacent to the cavity appeared coagulated and showed the same “wind-swept” nuclei seen with cautery artifact. Surrounding this was a white-tan ring that histologically showed recognizable tumor. No necrosis, increased apoptosis or inflammatory infiltrate was noted in this area on hematoxylin-eosin sections. Immunostains for cytokeratin were negative in the recognizable tumor cells despite intense staining in the epithelial cells outside the laser treated area. A ring of red tan tissue which histologically consisted of necrotic tumor was seen next and this, in turn, was surrounded by a rim of vascular proliferation and fat necrosis. The breast tissue outside the zone of fat necrosis appeared to be unaffected by the laser therapy.

Conclusions: ILT appears to be an effective way to treat small localized breast cancer. It is important for the pathologist to recognize the changes seen after ILT, especially the zone containing pseudoviable tumor. Cytokeratin may be a marker to identify these likely non-viable but recognizable tumor cells. The extent of the laser affected area is defined by vascular proliferation and fat necrosis.