Is Repetition of the Contralateral Mammogram of Patients Referred for Unilateral Findings from the Dutch Breast Cancer Screening Necessary? ()
1. Introduction
The Dutch screening program includes women from the age of 50 until 75. Screening mammograms are performed biannually in mobile units and minimally consist of bilateral two-view mammography (mediolateral oblique and craniocaudal views) [1]. These are then viewed by two independent radiologists to assess the need for referral to a dedicated breast cancer clinic. In case of discrepancies, a third (senior screening) radiologist makes the final decision.
When women are referred to a dedicated breast cancer clinic, Dutch guidelines still recommend repetition of the bilateral two-view mammogram, even when patients are referred for only one breast. Arguments for this approach are that images viewed on DVD or CDROM are not of diagnostic quality, but increase in sensitivity when abnormalities are imaged more often (for example, to rule out glandular tissue superposition), or in quality control of the hospital’s own hardware. These arguments, however, are debatable and not based on convincing scientific evidence. In contrast, repetition of the exam has several drawbacks: unnecessary patient discomfort [2], unnecessary radiation exposure, and increase in health care costs. Despite arguments in favor of repetition of the complete mammographic exam, repetition of the non-referred side does not seem to have any logical benefits, since the screening is digitalized in 2009. A study of Nederend et al. [3] showed that this improvement of quality led to a significant increased referral rate and cancer detection rate of the screening program. Therefore in this study, the aim was to evaluate the added value of repetition of the mammographic exam for patients referred from the Dutch breast cancer screening program for a unilateral suspicious lesion.
2. Materials and Methods
In the Netherlands, research covered by the Medical Research Involving Human Subjects Act must be submitted to an accredited medical ethics committee for approval. However, the Act does not cover retrospective research using (coded) data from patient’s medical record or patient images. Therefore, our medical ethics committee concluded that the research proposal of the current study does not, under Dutch law, require medical ethical approval (decision number: METC 11-4-137).
All digital (screening) mammograms were performed on a full-field digital mammography system (Selenia, Hologic Inc, Danbury, USA). The mammograms were performed according to a standard protocol, which includes a mediolateral oblique and craniocaudal view of each breast (special views are optional). The mean glandular dose (MGD) for the bilateral two-view mammogram exposed to the patient was 5.8 mGy (Standard deviation (SD) 1 mGy) (Information from the southern breast cancer screening region of the Netherlands, Eindhoven, Netherlands). With use of the breast tissue weighting factor 0.12, according to the International Commission on Radiological Protection (ICRP) 103 report, this MGD corresponds to an average effective radiation dose of (5.8 mGy × 0.12 breast tissue weighting factor) 0.7 mSv [4] . All screening mammograms were viewed by two independent experienced screening radiologists. In case of discrepancies, a third (senior) screening radiologists makes the final decision on referral or not.
The radiologists classified the findings according to an adapted version of the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) [5]. In the Dutch screening setting, findings can only be scored as being BI-RADS 0, 4 or 5. If the mammogram shows an abnormality, women are referred to a breast clinic of their choice.
We retrospectively collected all the data from women referred to our dedicated breast cancer clinic in a study period from October 2009 to August 2011. When referred, the bilateral diagnostic two-view mammogram was repeated for all patients on a full-field digital mammography system (Senopgraphe Essential, GE Healthcare, Waukesha, WI, USA), with a mean MGD for a bilateral two-view mammogram of 6 mGy (SD 1.1 mGy), which correlates with an average effective radiation dose of 0.72 mSv. Images of both breasts were reviewed and compared with screening mammograms by experienced breast radiologists.
In our work-up for these women, tissue superposition is suggested by performing the repeated mammography, a minimum of one additional special view of the area of interest, and a negative targeted ultrasound. Tissue superposition is confirmed as final diagnosis after six months of follow-up and an unaltered mammographic exam. If a cyst is suggested as cause for the referred abnormality, it is aspirated. A control mammogram should confirm the disappearance of the culprit abnormality. In all solid lesions (either benign or malignant), final diagnosis is made by image-guided large core biopsy. In general, a preoperative breast MRI is performed in breast cancer cases to assess tumour extent and evaluate the contralateral breast.
The anonymized data of all patients concerning the date of registration of the screening mammogram, the referred side (left/right or bilateral), age, screening BI-RADS, breast density, final diagnosis, biopsy results and breast MRI results was gathered in a database. Descriptive statistics were performed using the SPSS statistical software package, version 18.0 (SPSS, Chicago, IL, USA).
2.1. Retrospective Analysis of Contralateral Malignancies
To investigate whether newly detected contralateral lesions were (not) mammographically occult on screening mammography, all mammograms of the patients with contralateral breast cancer were retrospectively reviewed by an independent experienced radiologist (over 24 years of experience in screening and clinical mammography), who was blinded for every study results and aim. A validation set of 14 random mammograms from patients referred for confirmed unilateral breast cancer were added to this data set for blinding purposes. If a contralateral lesion was detected, the radiologist scored the mammogram using the regular BI-RADS classification [5]. If no contralateral lesion was depicted, the radiologist received the information of the preoperative breast MRI. With this information the radiologist retrospectively scored the lesion as being “occult”, a “minimal sign” or an “obvious finding” on both the screening mammogram and our institution’s mammogram.
2.2. Follow-Up
We registered the follow-up results of the enrolled patients and checked out the follow-up results for possible missed breastcancer in the contralateral breast. In the Netherlands during the 1-year after breast cancer diagnosis, follow-up consists of a physical examination every three months. In the second year the physical examination takes place every 6 months and in the third year only once a year. Every year also a bilateral two-view mammogram is performed.
3. Results
In our screening region, 31,901 women were invited for breast cancer screening from October 2009 to August 2011. A total of 28,112 women (88%) responded and of these, a total of 402 patients were referred to our dedicated breast cancer clinic. Seven patients were referred for bilateral suspicious lesions and were thus excluded from this study, leaving 395 patients referred for a unilateral suspicious lesion (Figure 1), with a mean age of 59 years (standard deviation (SD) 7.6 years).
Mean time between screening and institutional mammogram was 14.3 days (SD 3.3 days). Of the 395 patients referred for a suspicious unilateral lesion, no malignancy was detected in 245 patients (62%). In the remaining 150 patients, a unilateral malignancy was detected in 144 patients. In the remaining six patients an additional cancer was diagnosed in the contralateral breast (Figure 1). Table 1 provided additional information on which exams these cancers were visible and includes final histopathological diagnosis and size (case numbers are designated 1 to 6).
In case 1 to 5, bilateral breast cancer was detected. In case 6, no malignancy was detected on the referred side, but the cancer was detected on the contralateral side. Final diagnosis of these contralateral cases showed four invasive ductal carcinoma (IDC) with a mean diameter of 1.2 cm (SD 0.35 cm), and two ductal carcinoma in situ, with a mean diameter of 2.15 cm (SD 0.15 cm).
When re-evaluated by our institutional radiologists after referral, three contralateral malignancies were directly detected with the aid of the screening and institutional mammogram (cases 2 to 4). Case 2 consisted of a spicular mass in the contralateral breast, detected on both screen-
Figure 1. Women screened during a study period of 2 years and referred to our institution for diagnostic analysis.
Table 1. Findings of the screening mammogram, institutional mammogram and the breast MRI with the pathology results of the cases with a contralateral malignancy.
+: Suspect lesion, −: No suspect lesion, MG: mammogram, IDC: Invasive ductal carcinoma, DCIS: Ductal carcinoma in situ.
ing and institutional mammogram. Case 4 showed an irregular mass in the contralateral breast, detected on both screening and institutional mammogram. In case 3, our radiologist detected fine linear microcalcifications in the contralateral breast on the institutional mammogram, not on the screening mammogram. In case 5, no lesion was detected in both breasts on the institutional mammogram. A breast MRI was performed because of a discrepancy between the screening and institutional mammogram, which showed a bilateral breast cancer. Interestingly, all cancers were correctly identified with help of breast MRI, both ipsilateral and contralateral cancers (Table 1).
Figure 2 shows an example of a contralateral (minimal sign) lesion (case 1), overlooked with both the screening and institutional mammogram, but detected with breast MRI.