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Original Article |
1 Department of Surgical Oncology, C22, Canisius Wilhelmina Hospital, P.O. Box 9015, 6500 GS, Nijmegen, The Netherlands
2 Department of Medical Technology Assessment, Radboud University Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
3 Department of Pathology, Canisius Wilhelmina Hospital, P.O. Box 9015, 6500 GS, Nijmegen, The Netherlands
4 Department of Surgery, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021
Correspondence: Address correspondence and reprint requests to: Marjolein L. Smidt, MD; E-mail: marjoleinsmidt{at}yahoo.com.
| ABSTRACT |
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Methods: Patient, tumor, and SLN metastasis characteristics were collected for 222 consecutive patients who underwent a completion ALND. The data of the index and test populations were compared. A receiver operating characteristic curve was drawn, and the area under the curve was calculated to assess the discriminative power of the nomogram.
Results: Even though our patient population differed in many respects from the source population, the area under the receiver operating characteristic curve amounted to .77, a value very much comparable to the one found in the source population.
Conclusions: The nomogram provides a fairly accurate predicted probability for the likelihood of non-SLN metastases in a general population of breast cancer patients at a regional teaching hospital in The Netherlands. This suggests that the nomograms originally calculated predictive accuracy may be valid for patient populations that differ considerably from the population in which it was developed.
Key Words: Breast neoplasms Sentinel lymph node biopsy Nomogram Axillary metastases Prediction
| INTRODUCTION |
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A completion ALND is performed for staging, achieving regional control, and improving survival.913 Accurate staging requires information on the total number of nodes involved.14 Opponents of a routine ALND after tumor-positive SLN biopsy (SLNB) argue that the added therapeutic benefit is low.15 In earlier articles, only in approximately 50% of patients with metastatic disease in the SLN were additional nodal metastases detected in the completion ALND.16 A study on the follow-up of 31 SLN-positive patients who declined a completion ALND showed no axillary recurrences after a mean follow-up of 30 months. All patients had received adjuvant chemotherapy and breast and chest wall radiation.17 This is in accordance with the present guidelines, which recommend that virtually all SLN-positive patients should receive adjuvant chemotherapy. This, in combination with radiotherapy, might eradicate residual metastatic disease.18
After the introduction of the SLNB, several studies addressed the predictors of non-SLN metastases after a positive SLNB. To identify the individual patients risk for non-SLN metastases, a nomogram (Fig. 1
) was developed by the Breast Service of Memorial Sloan-Kettering Cancer Center (MSKCC; New York, NY). A nomogram is a graphical tool to depict a complicated calculation.19 The association of prognostic features with the likelihood of non-SLN metastases was assessed by multivariate logistic regression analysis of a retrospective group of 702 patients. The nomogram was created by using pathologic size, tumor type and nuclear grade, lymphovascular invasion, multifocality, estrogen receptor status, method of detection of the SLN metastases, number of positive SLNs, and number of negative SLNs. The outcome of the nomogram is the predicted probability of non-SLN metastases. This predicted probability can be determined graphically or, to facilitate use in daily practice and greater accuracy, can be calculated by the Web site http://www.mskcc.org/nomograms or through a personal digital assistantcompatible application. The nomogram was validated in a prospective set of patients from MSKCC: it reasonably accurately predicted the probability of non-SLN metastases for an individual breast cancer patient with a positive SLN at MSKCC. The aim of this study was to assess the nomograms generalizability by testing its predictive accuracy in a population of breast cancer patients from a regional teaching hospital in The Netherlands.
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| MATERIALS AND METHODS |
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SLN Identification
The SLN was identified by using 60 MBq of 99mTc nanocolloid as a radioactive tracer before surgery and 2 mL of blue dye (Bleu Patente V; Guerbet, Aulnaysous-Bois, France) for lymphatic mapping. During surgery, the SLN was harvested; this procedure was guided by the triple technique consisting of preoperative lymphoscintigraphy, blue lymphatic vessels, and detection of radioactivity by gamma probe (Neoprobe; Johnson & Johnson Medical, Hamburg, Germany).
SLN Histopathologic Examination
The SLN was bisected, after which both halves were embedded in paraffin. Each part was step-sectioned at 500-µm intervals at three levels and stained with hematoxylin and eosin (H&E) and immunohistochemical (IHC) staining. Cam5.2 is a mono-clonal antibody directed against cytokeratin 8, which is localized in the cytoplasm of the tumor cells (Becton Dickinson, San Jose, Calif). The nomogram differentiates three or four methods of detection of metastatic disease in the SLN: IHC only, serial, routine H&E, and possible frozen section. Because SLNs in this study were retrieved with use of local anesthesia, the nomogram without the frozen-section method of detection was used. No distinction was made in the database between serial and routine H&E, and all slides were reviewed by an experienced pathologist. If the first slide was positive, it was judged as routine H&E positive. Metastases found on further slides were judged as serial H&E or IHC positive, depending on the method of detection.
Data Analysis
Patient and tumor characteristics were collected from the prospective database for each variable of the MSKCC nomogram, including tumor type (ductal vs. lobular carcinoma), pathologic size (centimeters), and nuclear grade; presence of lymphovascular invasion; multifocality; estrogen receptor status; method of detection of the SLN metastasis (routine histopathology, serial H&E, or IHC); and number of positive and negative SLNs (Fig. 1
). These characteristics were compared with the prospective MSKCC data and tested for significance (Table 1
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| RESULTS |
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To assess the accuracy of the nomogram, actual probabilities were plotted against the calculated predicted probability for each decile of patients. The trend line shows almost complete concordance with the ideal line, with a slope of 1 (Fig. 2
). An ROC curve was drawn to assess the discrimination of the nomogram (Fig. 3
). The area under the ROC curve was .76 (95% confidence interval, .69.83). Both graphics and statistical analyses were repeated after exclusion of the patients in whom fewer than 10 lymph nodes were recovered. As a result, the calibration plot shifted to the left, and the area under the ROC curve amounted to .77 (95% confidence interval, .70.84; Fig. 4
).
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| DISCUSSION |
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Because the nomogram was developed in MSKCC, which is a tertiary referral center, the question arose whether it would be applicable to the population of a Dutch regional teaching hospital. The difference of the studied populations was reflected in significantly deviating patient and tumor characteristics. The area under the curve, however, amounted to .76 in the Dutch population for the entire group and to .77 for the group comparable to the source group. For the New York group, the area under the curve was .78. The scale of the area under the curve ranges from .5 for a test as good as the toss of a coin to 1.0, which makes a perfect test. An area under the curve of .77 is therefore a reasonably accurate predictive test.
According to the MSKCC inclusion criteria, at least 10 lymph nodes need to be retrieved. This criterion was not met in 24% of the Dutch patients. The likelihood for detecting a non-SLN containing metastatic disease increases with the number of examined nodes. A higher yield of nodes per patient would therefore result in a shift of the calibration plot to the left. Our data suggest, however, that the influence of the number of retrieved lymph nodes is minimal and that this should not preclude use of the nomogram.
Recently a study was presented that compared surgeons predictions of the probability of non-SLN metastatic disease with the performance of the MSKCC nomogram. The surgeons predictive accuracy corresponded with an area under the curve of only .54. Clearly, the MSKCC nomogram outperformed expert judgment, thus emphasizing its clinical utility.32
The observed differences in patient populations can be explained by the function of the hospitals: MSKCC is an oncological referral center, and the Canisius Wilhelmina Hospital is a regional teaching hospital for the general population. The higher incidence of smaller tumors at MSKCC could be the result of annual screening for breast cancer in all patients, compared with the Dutch screening scheme, which consists of 2-yearly screening of women aged 50 to 75 years. Approximately 30% of the study patients had a screening-detected tumor. Except for size, all tumor characteristics had a better profile in the Dutch population, which corresponds to a more general patient population mix.
A subset of 40% of the 50% of breast cancer patients with an SLN containing metastatic disease will have non-SLN metastases. Consequently, a cutoff value of 10% predicted probability would concern 2.0% of all patients. According to the predicted probability of 10%, only .2% would be at risk for residual metastatic disease in non-SLNs. Axillary recurrence rates after negative SLNB are so far lower than expected. This may be explained by the increasing number of patients in this group receiving adjuvant therapy.18,33 Patients with an SLN containing metastatic disease will always be considered for adjuvant therapy. As a consequence, axillary recurrence rates will even be lower than expected, and a cutoff point of 10% seems therefore reasonable and defensible. In current practice, the nomogram was used to avoid completion ALND in several patients with a low likelihood (<10%) of non-SLN metastases. The Dutch guidelines, however, recommend a completion ALND for all patients in the presence of only one prognostic factor: a positive SLN. This nomogram enables the formation of an individualized risk estimate for the probability of non-SLN metastases based on eight predictors. The nomogram does not make a statement on treatment recommendations. Its results can support the multi-specialty oncological team as well as the doctor or patient regarding the choice of whether an ALND is desirable, taking into account, for instance, patients preferences and risk aversiveness. Further research on estimates of non-SLN metastases by oncologists versus the MSKCC nomogram is warranted.
In conclusion, the nomogram provides a fairly accurate prediction of the probability of non-SLN metastases in a general population of breast cancer patients differing from the population in which the nomogram was originally developed. The resulting risk estimate can help to individualize a patients treatment.
| ACKNOWLEDGMENTS |
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Received for publication July 21, 2004. Accepted for publication July 29, 2005.
| REFERENCES |
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