The current guidelines do not recommend regular surveillance chest CT for breast cancer survivors. However, patients’ fear of recurrence and clinicians’ inclination toward early detection of disease recurrence results in frequent usage of systemic imaging [18]. In a previous survey of medical and surgical breast oncologists conducted by the Korean Breast Cancer Society, 50% of respondents indicated that they perform follow-up chest CT more than once annually in the first 5 years [10].
Occult breast lesions may be incidentally revealed during CT. Although CT has limitations due to radiation exposure, it is a faster and more comfortable imaging modality than MRI. CT can be an alternative when MRI is unavailable, such as in cases of claustrophobia or the presence of a cardiac pacemaker [19]. Various studies have investigated breast lesions detected in chest CT. Tumor size on chest CT correlates well with pathologic tumor size in patients with breast cancer. Features such as irregular shape, spiculated margin, and rim enhancement on CT images have been reported as predictive of malignancy [20–22]. However, another study reported that there are no definitive criteria to differentiate benign from malignant lesions [23]. A recent study investigated the quantitative enhancement value of chest CT for distinguishing between benign and malignant lesions, with malignant lesions demonstrating higher degrees of enhancement [24].
Unlike MRI, which provides sequential dynamic enhancement, chest CT typically involves only one phase acquisition, which is available after contrast media administration. Usually, a scan delay of 55–70 s is maintained following contrast administration on chest CT, corresponding to the early dynamic phase on MRI [25]. Inoue et al. evaluated the time-intensity curve of dynamic multidetector-dedicated breast CT with four acquisitions (pre, 1, 3, and 8 min), indicating that the washout and plateau pattern between 3 and 8 min had a high positive predictive value (93%) for malignancy [22]. Abbreviated MRI, which only acquires early enhancement within 2 min without delayed enhancement, has been used frequently recently, and its diagnostic ability is not inferior to that of full dynamic MRI [26]. While delayed dynamic enhanced images cannot be obtained from chest CT, images obtained only from the early dynamic enhancement phase still play a role in detecting recurrence.
In this study, only 58 out of 89 recurrent tumors were identified, although the radiologists had information about tumor locations. Without knowing the location information, 50 and 56 recurrent tumors were found with a substantial degree of inter-observer agreement. Unlike other studies, this study included only patients diagnosed with recurrence. Despite all patients having a recurrence, specialized radiologists could not identify the tumor on chest CT in 34% of cases. Therefore, while chest CT may serve as a complementary modality for discovering breast cancer recurrence, it is not completely reliable for identifying all recurrences.
The pathology and tumor presentation type of the current episode of second breast cancer on chest CT and MRI differ between the visible and non-visible groups. The use of contrast media enables the detection of breast cancer because breast cancer has an increased contrast media uptake compared with breast parenchyma because of neovascularization [27]. Breast cancers develop an increased capillary network and increase vascular permeability through their release of certain angiogenic factors, primarily vascular endothelial growth factor (VEGF), which induces both the proliferation of pre-existing capillaries and the formation of new vessels. These factors contribute to their earlier and more intense contrast enhancement than that of normal fibroglandular tissue [28, 29]. In this study, IDC is more visible than ductal carcinoma in situ (DCIS) on chest CT, likely because lower neovascularization has been observed in DCIS, which may account for the non-visualization of some DCIS [20, 30]. In a study by Schnall et al. [31], 16% of DCIS lesions and 3% of invasive carcinomas demonstrated no enhancement on MRI. This may also explain why mass-type tumors are more visible on chest CT. Non-mass-type breast cancers have a lower histological grade and are closely related to DCIS components [32].
On chest CT, recurrent tumors in fatty backgrounds are more visible than those in glandular tissues. Both glandular tissues and masses appear dense on chest CT and can only be detected if masses are enhanced, but the masses located in the fatty background are easier to detect due to the clear contrast with the surrounding fat [33].
Logistic regression was performed to determine which patient group could better detect recurrent cancer on chest CT using previous clinical pathology data. The analysis revealed that recurrent cancer is more easily detected on chest CT in patients who had previously undergone mastectomy. This finding is likely related to the fact that tumors located in a fatty background are more easily identified, as observed in this study. Previous studies have reported recurrence rates following mastectomy ranging from 3.6–7.7% [34–37]. In many cases, mammography is technically challenging, and its sensitivity for detecting recurrent tumors is inferior to that of physical examination [38], often relying on ultrasonography or MRI [39–41]. A meta-analysis of surveillance imaging post-mastectomy reported that the overall cancer detection rate per 1000 examinations was 1.86 (95% CI, 1.05–3.30) for mammography, 2.66 (95% CI, 1.48–4.76) for ultrasonography, and 5.17 (95% CI, 1.49–17.75) for MRI [42]. However, in the clinical setting of surveillance post-mastectomy, the rates of clinically occult, nonpalpable cancer were considerably lower than cancer detection rates across all imaging modalities [42]. In asymptomatic patients, conventional surveillance imaging should be performed carefully. This study has some limitations. Our study did not include negative cases. The participating radiologists were aware that the patients in this study had breast cancer. This preconceived notion may have led to the overdetection of breast cancer that might have been overlooked under routine reading conditions. This is a single-center study with a small sample size. Due to the relatively low proportion of patients presenting with isolated breast recurrence, single-institution studies will always be limited by sample size. The results of this study can be validated by performing surveillance workups using chest CT in clinical practice. Therefore, a multicenter prospective study with a larger sample size is needed.