Following an intitial breast cancer screening mammogram, there are two situations in which a woman may be asked to return for a 'follow-up' mammogram. First, if something abnormal is found on the X-ray, it is likely that a woman will be called back for additional imaging studies. This is sometimes called a 'diagnostic' mammogram, even though in most cases no disease will be diagnosed per se. Secondly, there could be a totally normal or benign finding, but with evidence that a women remains at increased risk for breast cancer development. Follow-up mammograms and clinical evaluation in high risk women tends to be a little more rigourous and with a shorter interval.
Following the initial screening, there will be a certain percentage of women who may be considered as having a higher risk, even if the results are clear. Women with atypical ductal hyperplasia or lobular neoplasia , as revealed by surgical biopsy, should naturally be rescreened at regular intervals. Also, women with a high probability of having a having a cancer-predisposed gene are at higher risk. For example, if there is breast cancer or ovarian cancer in first or second degree family members, especially occurring before the age of 40, or if a women has a genetic predisposition as revealed with a molecular exam, then there ought to be close follow-up. It is also estimated that women who carry the BRCA1 and BRCA2 mutations are at an increased risk for breast cancer development with risk estimates ranging from 40%-80%. These individuals would likely be recommended for follow-up mammograms every 6 months to 1 year.
Quite often the most prudent measure for a very low risk finding is simply to 'observe' the suspected lesion on subsquent mammograms, at intervals ranging from six months to a year generally. The number of women asked to return for a follow-up mammogram will vary in different countries and districts to a certain extent.
Mammograms are typcially read at least twice. If the intitial result is 'positive', the radiologist will usually request typical follow-up procedures such as magnification, fine needle aspiration , and ultrasound. All films will be read by a second expert. Note, the "standard" definition of false positive result in breast-cancer screening implies a one-year period. If there is no confirmed diagnosis of breast cancer up to one year after the intial abnormal rescult, that result will be termed 'false positive'.
A screening physician (radiologist) has to be quite careful how impressions are interpreted and expressed, when requesting a follow-up mammogram. A great deal of unnecessary anxiety can be caused by the term 'positive result' on a screening mammogram. It is not a postive result until breast cancer is confirmed, and by a wide margin, most 'abnormal' results on a first breast cancer screening mammogram end up being benign, or 'negative' for breast cancer. (At least, in the first year of screening. Positive results at screening in subsquent annual examinations are more likely to be breast cancer).
It is estimated that over a 10 year period, about one third of women called-back for a 'diagnostic' (second) mammogram will have benign breast disease, or in other words a 'false positive' reading. However, these are statistics taken over time, with annual or biannual mammograms. When a women is called back for a follow-up mammogram after several years of regular breast cancer screening, the changes of abnormal findings actually being indicative of breast cancer will naturally increase.
About 9% of women who have something abnormal on their first mammogram still do not report for follow-up mammograms, which is unfornate. Factors associated with failure to report to a follow-up mammogram include low socio-economic status and low levels of formal education. Women who perceive a higher than average level of cancer in their extended family tend to be the most motivated to attend a follow-up mammogram. But there can still be anxiety associated with a follow-up mammogram. About 26% of women asked to return for a follow-up mammogram after the initial breast cancer screening express high anxiety over the possibility of breast cancer. Of course, a majority of follow-up mammograms turn out to be benign breast disease. There is no doubt that an abnormal mammogram and subsquent call back mammogram can cause increased anxiety for women for an extended period of time, even when the second mammogram (or biopsy) confirmed negative.
Short term follow-up mammography has long been advocated as a reasonable approach in the management ot nonpalpable breast lesions detected on a breast cancer screening mammogram, and in particular for those breast lesions which appear 'likely benign' due to their imaging characteristics. The alternative would be to request a biopsy sample from the patient, though in most cases a percutaneous biopsy would be sufficient. But in general the cost savings of a follow-up mammogram instead of a biopsy for 'probably benign' breast lesions is considerable, and statistics have not indicated any appreciable difference in the number of 'false-negative' breast cancer diagnoses. The thing to remember is, by a vast majority, lesions detected by the intital breast cancer screening mammography are in fact benign.
It can be a challenge to find reasonable and balanced cutoff points in deciding first whether follow-up diagnostic mammogram is even warranted, and secondly whether or not a biopsy should be used instead. Generally speaking, if the first screening mammography results are interpreted as 'highly suggestive of malignancy', then a core-needle biopsy should probably be the next step. When the initial mammogram reveals an abnormality that is interpreted as 'probably benign', then additional imaging is generally required in order to decide whether to biopsy or not. Specifically, the radiologist will want to determine whether the lesion is a solid mass or more of a cyst, and will also probably want to take a closer look at the margins. If all indications of the second imaging studies are for a benign or likely benign lesion, then subsequent follow up imaging studies in about 6 months is probably a reasonable approach, without the necessity of microscopic evaluation.
About 92% of screening mammograms do not require additional follow-up imaging. One cannot generalize about the number of follow-up mammograms that will require biopsy, as this totally depends upon the specifics of the lesion in each individual case. However, it can be stated that about 60%-70% of women who go through a follow-up diagnostic mammogram or ultrasound, and, have imaging features abnormal enough to require a biopsy, will turn out to have benign breast disease only. About 30% of these women may in fact have breast cancer.
One should not over-analyze the steps taken by the screening and diagnostic team. The evaulative procedures for breast cancer are well documented and basically standardized, and the physicians will only be asking for prudent diagnostic measures. However, it is fair to say that if only a follow-up ultrasound is requested, the radiologist is in most cases pretty sure that it is not breast cancer (most likely a cyst), and only about 12%-17% of these suspicious lesions turn out to be breast cancer. If the diagnostic follow-up asks for a second mammogram as well as ultrasound, the lesion turns out to be breast cancer about 20% of the time. When the doctors request a follow-up diagnostic mammogram, and an ultrasound, and a biopsy, the suspicious mass turns out to be breast cancer about 37% of the time.
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