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A significant clinical problem in the local treatment of cutaneous
metastases of breast cancer (by any modality--surgery, radiation
therapy or photodynainic therapy) is the fact that the disease almost
always extends beyond the boundary of visible lesions in the form of
microscopic deposits. These deposits may be distant from the site of
visible disease but are often in close proximity to it and are
manifested sooner or later by the development of recurrent lesions at
the border of the treated area, thus the "marginal miss" in radiation
therapy, the "rim recurrence" in photodynamic therapy, and the
"incisional recurrence" following surgical excision. More intelligent
use of these treatment modalities demands the ability to detect
microscopic deposits of tumor cells using non-invasive methodology.
In vivo fluorescence measurements have been made possible by the
development of an extremely sensitive fiber optic in vivo fluorescence
photometer. The instrument has been used to verify that fluorescence
correlated with injected porphyrin levels in various tissues. The
delivery of light to excite and detect background fluorescence as well
as photosensitizer fluorescence in tissues has been accomplished using
two HeNe lasers emitting at 632.8 nm and 612 nm delivered through a
single quartz fiber optic. Chopping at different frequencies,
contributions of fluorescence may be separated. Fluorescence is
picked up via a 400 micron quartz fiber optic positioned appropriately
near the target tissue. Validation of these levels was made by
extraction of the drug from the tissues with resultant quantitation.
Recently, an extensive study was undertaken to determine if
fluorescence could be used for the detection of occult, clinically
non-palpable metastases in the lymph node of rats. This unique model
allowed for the detection of micrometastases in lymph nodes using very
low injected doses of the photosensitizer Photofrin II. Data obtained
revealed the ability to detect on the order of 50-100 cells using 0.25
mg/kg of sensitizer, a level 20 times lower than normally used for
treatment of animal tumors. These results indicate that Photofrin II
could be used for fluorescence detection of small metastatic tumors,
while substantially reducing the major side effect of PDT; namely,
prolonged photosensitivity. Results to be presented demonstrate the
ability of this technique to detect microscopic deposits of malignant
tumor cells in patients with metastatic breast cancer. These deposits
were found in clinically negative areas of the chest wall.
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