False-negative Frozen Section of Sentinel Lymph Node Biopsy in a Chinese Population with Breast Cancer

Discussion

SLNB is a minimally invasive procedure to determine the presence of ALN metastases in patients with clinically negative nodes. Although patients undergoing ALND have higher morbidity than that associated with SLNB, current guidelines still advocate ALND if SLN metastases are found, except for patients that fit the American College of Surgeons Oncology Group Z0011 criteria (6). An accurate intraoperative diagnosis of SLN metastases is therefore very important in order to avoid reoperation for patients with positive SLNs and spare them additional costs.

Among the various methods of intraoperative SLN assessment, FS is the most commonly used. Many studies have evaluated the sensitivity and accuracy of intraoperative FS. A meta-analysis reported sensitivity of intraoperative FS, ranging from 57-74% (3). According to another meta-analysis (7), the mean sensitivity was 73%, mean specificity 100%, and intraoperative FS was more reliable for detecting macrometastases than for detecting micrometastasis/ITC deposits (7, 8). In addition, the touch IC method was also used widely. The greatest advantage of touch IC lies in its technical simplicity, low cost and total tissue preservation. But an accurate interpretation of the imprint is often limited by low cell yield and requires a pathologist experienced in cytological analysis. A meta-analysis that evaluated intraoperative IC for SLNs indicated that the pooled sensitivity was 63%, and its specificity was 99% (9). Hence FS evaluation is slightly superior to touch IC because it is more sensitive and less likely to produce an equivocal inconclusive result. Intraoperative FS may be the most desirable method for experienced teams of surgeons and pathologists (10). Molecular techniques such as ultrarapid immunohistochemistry using antibodies to cytokeratin, reverse transcription-polymerase chain reaction and one-step nucleic acid amplification analysis have also been used to facilitate detection of nodal metastasis especially for the detection of micrometastases (11, 12). However, the sensitivity of molecular techniques remains limited by the number of sections available/required for analysis, and a false-negative result is still possible because examination of every level of the entire SLN is infeasible. The possibility of contamination with RNA and the lack of morphological validation have raised questions about the clinical significance of a positive result. Multiple step-section FS analysis of SLNs is a relatively cost-effective alternative to molecular technologies and more accurate than standard FS or touch-prep cytology. But its disadvantage lies in the fact that a large number of scientists and consultants may be required in order to process multiple lymph nodes within a reasonable time (13). For these reasons, neither IC, molecular techniques nor multiple step-section FS was routinely used in our Institute.

• Download figure
• Open in new tab
• Download powerpoint

Figure 1.

The recurrence-free survival rate of the patients with false-negative sentinel lymph node biopsy did not differ from that of patients who had a truly negative SLNB (p=0.072).

• Download figure
• Open in new tab
• Download powerpoint

Figure 2.

The overall survival was statistically different between patients with false-negative sentinel lymph node biopsy (SLNB) and those with truly negative SLNB (p=0.035).

As outlined above, FS is now the preferred method for the detection of nodal metastases. However, the greatest drawback is the frequency of false-negative results because of which these patients are still subject to recall for ALND. Some reports revealed false-negative rates of FS ranging from 13% to 43% (14, 15) and false-negative results occurred more frequently in cases with micrometastases (15-18). In our study, FS had a false-negative rate of 15.3%, and 83.0% of metastasis were less than 2 mm in size. Although this was lower than most studies, we believe that if all SLNs were bisected longitudinally for diagnosis separately it might be more effective in reducing the false-negative rate.

Which factors can predict SLN metastasis and false-negative FS? Univariate and multivariate analyses showed that tumour size, location, type and lymphovascular invasion (LVI) were independent predictors of SLN metastasis (19). Another study revealed that LN-positive tumours were most frequent in the younger age group (<50 years). Among the immunohistochemistry-based individual biomarkers (ER, PR, Ki-67, HER2), only HER2 status was significantly predictive of lymph node status (20). Different breast cancer molecular subtypes have different biological features. Van Calster et al. showed that triple-positive tumors are most likely to be lymph node positive (21). Luminal A and triple-negative breast cancers are the least likely to present with positive lymph nodes. The imaging findings can also predict lymph node metastasis and prognosis. Among tumours smaller than 1 cm and measuring 1.0-1.4 cm, fewer cases of positive lymph nodes occurred in those with stellate lesions (22). But Tabar et al.'s study revealed that positive nodes were found in 12.23% (45/368) of lesions in the group of patients with stellate tumour without calcifications compared with 11.81% (30/254) of lesions in the group comprising the other patterns combined (4). They also found that casting-type calcifications were associated with a positive lymph node status, poorer histological grade and an increased risk of death. Moreover, after clinical follow-up, patients with stellate tumours had a better survival prognosis than those with tumours with other patterns (4, 22).

A few studies have tried to determine the predictors of false-negative FS. For these false-negative cases, an invasive lobular histology and LVI were found to be independent predictors on multivariate analysis (14). Another study also reported a higher false-negative FS rate for invasive lobular compared with invasive ductal carcinoma (23). But at least one study reported comparable results (24). The reason may be that invasive lobular tumor cells resemble benign lymphocytes and histiocytes and are more easily missed because of their bland cytological features and discohesive infiltrative pattern (23). In the study of Takei et al. patients with an intraoperative, false-negative SLNB had a combination of favourable and unfavourable prognostic factors compared to patients with negative SLNB. The favorable prognostic factors were positive PR and low nuclear grade, while an unfavourable prognostic factor was positive LVI (25). A recent study revealed that non-ductal histological subtype, absence of LVI and the size of SLN metastasis were independent factors associated with a higher false-negative rate compared with true-positive cases (26). As in our study, the favourable prognostic factors were positive ER and PR status and an unfavourable prognostic factor was a young age. We also found a new predictor: stellate mammographic pattern. Patients with stellate mammographic pattern were more likely to have false-negative FS result. Why these two groups exhibit such different characteristics remains unclear.

Another question is whether these false-negative cases need reoperation. One study showed that 94% (31 out of 33 specimens) of metastatic foci were found in the subcapsular sinus of the lymph node in false-negative cases (26), which implied that lymph node dissection may be safely avoided. Of our 45 patients who underwent a further different level ALND, additional non-SLN metastases were found in only four (8.9%) patients. That is to say that most patients (91.1%) were not required to undergo an additional operation. With a median follow-up of 29 months, only one patient exhibited recurrence in the axillary nodes. Takei et al. showed that none of their 132 patients with intraoperative, false-negative SLNBs experienced recurrence in the axillary or other regional nodes, with a median follow-up period of 58.1 months (25). Based on these data, we believe ALND can be avoided in most cases with intraoperative false-negative SLNB, which is agreement with Takei et al. (25). We also found the false-negative FS cases had poorer prognosis than patients with true-negative SLN after clinical follow-up.

Radiotherapy can effectively control local recurrence. A meta-analysis showed that axillary radiotherapy might be an alternative strategy to ALND (27). Non-randomized studies have also shown that axillary radiotherapy might be an effective and safe alternative to ALND for the treatment of the axillary (28). From this point of view, axillary radiotherapy might be an effective strategy substitute for ALND for some high-risk patients with false-negative FS of SLN.

The limitations of this study include a small sample size, its retrospective nature, and the short follow-up time. Future prospective studies with a large sample size are needed to validate our findings.

In conclusion, FS was useful for the detection of nodal metastases in SLNs. The main failure of FS was in detection of micrometastases and ITCs. Younger age, stellate mammographic pattern and positive ER status were independent predictors for false-negative FS. ALND can be avoided in most patients with intraoperative, false-negative SLNB.