Introduction
The introduction of mammography (MMG) as an adjunct in breast screening examination has increased the detection frequency of ductal carcinoma in situ (DCIS). At the same time, breast ultrasonography (US) examination in women with dense breast tissue has led to the detection of breast cancers that were not identified on MMG. The frequency of breast cancses detected by US is approximately 0.3–0.4%. US has been frequently reported to be more sensitive than MMG [
1‐
3], and many DCISs have been detected by US. However, currently there is no definite opinion on US findings of DCISs, which have been reported as irregular masses, mammary duct ectasia [
2,
4,
5], and benign cystoids [
1,
5]. Furthermore, in these reports, many cases that are detectable by MMG were included. We performed US in all outpatients that visited our clinic, and those with positive findings underwent detailed examination mainly via aspiration biopsy cytology. As a result, we could detect many DCISs by US alone [
6]. In this study, we summarize the features of DCISs detected by US alone based on US and clinicopathological findings.
Patients and methods
From January 2003 to December 2007, we examined 35,886 women. Of those, 2,812 masses were sampled by ultrasound-guided fine-needle aspiration cytology. We found 729 cases of primary breast cancers at our clinic, of which 150 cases (20.6%) diagnosed with pathological DCISs were included in this study. They were retrospectively classified by one author into cases detected by US alone (echo group) and cases detected by MMG or clinical findings, such as palpable mass and abnormal nipple discharge (MMG/PE group), and examined clinicopathologically. The following US devices were used: ALOKA-SSD1000, ALOKA-SSD5000, TOSHIBA XARIO, and APRIO. In all cases, MMG and US were performed regardless of age. Cases with shape irregularities, internal echo irregularities, segmental and solitary cystic lesions in the elderly, etc., on US examination were examined in detail [
6] regardless of tumor size. For cases that required detailed examination and those in which lesions were observed by US, aspiration biopsy cytology was performed using a 23 G needle.When MMG revealed calcifications and the lesions could not be determined by US, mammotome biopsy was performed. For pathological investigation, the resected specimens were cleaved at 2–5-mm intervals, and sections were prepared. For classification of DCIS histological subtypes, comedo necrosis of ≥50% of the gross tumor was categorized as comedo type and the others as non-comedo type. For the assessment of extensive intraductal components, those located ≥2 cm from the periphery of the main lesions recognized by US were defined as positive. For the pathological classification of DCIS, Van-Nuys classification [
7] was used. The US and clinicopathological findings were statistically analyzed by χ
2 analysis and
t test.
Discussion
Through a wider use of MMG, the frequency of DCIS detection is increasing [
9‐
13]. While many DCISs are detected through microcalcifications [
11‐
13], those without calcifications cannot be detected by MMG, and 6–23% DCIS are said to remain undetected [
5,
11‐
15]. At the same time, by breast US, smaller breast carcinomas can be detected than by MMG alone, and a high breast carcinoma detection rate (0.31–0.4%) has been reported in which the frequency of DCISs was 11–14% [
1‐
3]. US, in particular, is believed to be useful for detecting breast carcinomas in young people with dense breast tissue [
1‐
3]. However, as most DCISs detected by US that have been reported so far were comedo type, many of them were also observed as abnormal by MMG and frequently accompanied by subjective symptoms [
6,
12‐
14,
16]. We performed US in all outpatients that visited our clinic, and those with positive findings underwent detailed examination. As a result, many DCISs without subjective symptoms could be detected by US alone [
7].
In this study, we examined 150 cases with DCIS using US and retrospectively classified them into a cystic or solid mass, ill-defined hypoechoic mass, microlobulated mass, duct dilatation, and calcification. Among these, in 37 (79%) of 47 cases with US findings alone, a cystic or solid mass was observed. Most were ovoid in shape, and the margins were circumscribed or microlobulated, making it difficult to differentiate from benign lesions. Moreover, approximately half of these cases had heterogeneous internal echoes.
Moon et al. [
6] reported DCISs detected by US; however, they performed US in subjects with dense breast tissue and subjective symptoms, and almost all cases had calcifications. Thus, this study cannot be compared with ours. Chen et al. [
16] reported that non-comedo type DCISs are characterized by irregular margins, a non-uniform internal echo texture, and an anteroposterior diameter/width ratio of ≥0.7; however, they were all palpable lesions, 35% of which had calcifications, and thus, the findings of this study deviates from our results. On the other hand, recent reports on high-resolution US make it likely that DCISs that we classified as cystic and solid lesions in this study correspond to the solid and cystic lesions comprising single or multiple hypoechoic masses described by Moon et al. [
6] and to “Apart from the small size of the nonpalpable and mammographically occult lesions: complex cysts” described by Wolfgang [
1]. However, these reports also deal with non-palpable cystic or solid masses and DCISs with shapes similar to that of benign lesions, and it is not mentioned that 79% of findings accounted for masses detected by US alone. US findings of DCISs manifesting solid and cystic masses are characterized by those observed in benign diseases, and it is difficult to differentiate DCIS detected by US alone from benign diseases [
1,
2,
6]. In the present study, there were many cases in which it was difficult to differentiate DCISs from benign lesions based on shape, margins, etc., and it appeared necessary to conduct detailed investigation mainly via aspiration biopsy cytology.
In this study, mass diameters of the echo group were half that of the MMG/PE group and consistent with those in other reports [
1,
17,
18]. Furthermore, localized lesions with few extensive intraductal components were frequently observed, and the Van Nuys classification [
8] tumor grades of the echo group were significantly low. In the echo group, all cases with lesions of <5 mm were Van Nuys classification grade 1. Tumor grades were also significantly low compared to those of lesions ≥5 mm of the MMG/PE group. In addition, comparison of cases with lesions ≥5 mm in both groups showed that tumor grades of the echo group were lower than those of the MMG/PE group.
This suggested that cases with lesions of <5 mm detected by US alone can be successfully treated by local resection [
19,
20]. The prospective study by ultrasound findings will be necessary in the future. Determination of the course of treatment of such lesions is a subject of future investigation.
DCISs detected by US alone were of low tumor grades when classified by Van Nuys classification and were characterized by frequent localized lesions with few extensive intraductal components, suggesting the possibility of successful treatment by local resection.