Our study demonstrates that frozen section is superior to imprint cytology for the intra-operative diagnosis of sentinel node metastasis. Frozen section had a higher sensitivity than imprint cytology, while its high specificity was comparable to that of imprint cytology.
Several reports in the literature have compared frozen section with imprint cytology, and most of these reports have recommended imprint cytology for intra-operative sentinel lymph node determination. [4
] Imprint cytology is considered a rapid and convenient method with sensitivity and specificity similar to that obtained with frozen section. However, as seen in Table , which presents comparisons of sensitivities and specificities obtained from various reports, the sensitivity of imprint cytology is likely to be lower than that of frozen section. [6
] Although some studies showed good sensitivities for imprint cytology, these investigators either did not investigate frozen sections [7
] or they studied more sections using imprint cytology than using frozen section. [6
Reported results of intraoperative imprint cytology and frozen section
The characteristic feature of our study is that we compared imprint cytology and frozen section in an equal manner, because we studied the same sectioned surfaces using both methods. As a result, our data showed that the discrepancy in the sensitivities between these methods could be attributed mainly to sampling error associated with the imprint technique.
The evaluation of specificities in imprint cytology is also a complex issue. Generally, it is difficult to achieve a specificity of 100% using imprint cytology. There are at least two possible explanations for this difficulty. First, it is possible that benign specimens may be judged as containing malignant cells. In particular, the lobular type of breast cancer is believed to generate a false positive on imprint cytology due to the small and bland morphology of the cells. This means that some patients may undergo unnecessary axillary dissection. Unwarranted axillary clearance is clearly more problematic than a second operation for axillary dissection. The second reason is associated with micro-metastases. In cases of micro-metastases, it is possible that only imprint cytology can detect metastatic cells. However, when histopathological evaluation is required to define sentinel lymph node metastasis, the role of imprint cytology is limited.
For these reasons, we recommend frozen section rather than imprint cytology for the intra-operative diagnosis of sentinel lymph node metastasis.
We initially attempted to use imprint cytology as a modality complementary to frozen section for the intra-operative diagnosis of sentinel lymph node metastasis. Therefore, we used the Papanicolaou method for intra-operative cytological evaluation. Although this technique is time-consuming compared with other staining methods, we believe this procedure is greatly advantageous because it results in accurate evaluations.
The rate of positive sentinel node detection in patients with a sentinel node biopsy in our cohort is likely to be lower than that reported in other studies. The use of trisecting, which is nowadays inappropriate for the analysis of sentinel nodes, may be responsible for this result. However, we believe that ultrasonography, which was used in addition to physical examination to evaluate preoperative nodal status at our institution, contributed significantly to this consequence by allowing us to obtain more accurate nodal evaluations. The rate of positive sentinel node detection in patients who received a sentinel node biopsy should be low, because a high positive rate increases the possibility of missing axillary node metastases, both in sentinel and non-sentinel nodes. This, then, increases the likelihood of a subsequent salvage operation after swollen axillary lymph nodes become clinically apparent.
In the intra-operative diagnosis of lymph node metastasis, the management of micro-metastases is a difficult problem to solve. [8
] Several new intra-operative approaches to micrometastases have been reported. [21
] Their approaches are based on intra-operative thin sections, in which the nodes are examined thoroughly on the basis of frozen section. These time- and money-consuming methods are less likely to be introduced to routine clinical practice. The long-term prognostic impact of micro-metastasis should be established as soon as possible.