Invasive lobular carcinoma (ILC) is the second most common histologic subtype of breast cancer, accounting for 5% to 15% of all cases. Unlike invasive ductal carcinoma (IDC), ILC has an infiltrative growth pattern that makes detection challenging with traditional screening methods. Its lack of cell cohesion and tendency to grow in single-file lines often result in subtle or absent architectural changes in mammography. Consequently, ILC is frequently diagnosed at more advanced stages, with larger tumour sizes and a higher likelihood of multifocal or bilateral disease. The limitations of standard imaging techniques necessitate advancements in screening approaches to improve early detection rates and patient outcomes.
Challenges of Detecting ILC in Mammography
Mammography remains the first-line imaging modality for breast cancer screening, yet its sensitivity for ILC is lower than for IDC. ILC often lacks the typical spiculated masses or calcifications seen in IDC, instead presenting as architectural distortions, asymmetries or even normal-appearing tissue. Studies show that 77.5% of ILCs are retrospectively visible on prior mammograms, highlighting their subtle presentation. Additionally, ILC is more likely to be diagnosed as an interval cancer, meaning it is detected between scheduled screenings rather than during routine mammography. The sensitivity of mammography further declines in women with dense breast tissue, where ILC can remain masked by overlapping fibroglandular structures.
To address these limitations, digital breast tomosynthesis (DBT) or 3D mammography, has been introduced as an adjunct to standard digital mammography (DM). DBT improves the conspicuity of ILC by reducing tissue overlap and enhancing the detection of architectural distortions. Large screening trials have demonstrated that DBT increases sensitivity for ILC, particularly in women with dense breasts, with reported improvements in detection rates ranging from 75% to 92%. Despite these advances, a proportion of ILCs remains undetected, necessitating supplemental screening methods.
The Role of Ultrasound in Supplemental Screening
Ultrasound (US) serves as a valuable supplemental imaging tool, particularly for women with dense breasts or those at increased risk of breast cancer. Unlike mammography, US is not affected by breast density and is effective in identifying cancers that are mammographically occult. The most common US appearance of ILC is a hypoechoic irregular mass with posterior shadowing. However, up to 39% of cases present as non-mass lesions, making them more difficult to recognise.
Studies have demonstrated that screening US detects additional ILCs after negative mammography or DBT findings. In a large screening study, ILCs accounted for 13% of cancers identified exclusively by US. Furthermore, interval cancers with ILC histology were found to decrease when US was included in screening protocols. Handheld ultrasound (HHUS) and automated whole-breast ultrasound (ABUS) have shown similar detection rates for ILC, with ABUS offering the advantage of reproducibility and reduced operator dependency. However, despite its benefits, US is limited by a higher false-positive rate and challenges in distinguishing ILC from benign lesions.
MRI and Emerging Modalities for ILC Detection
Magnetic resonance imaging (MRI) is the most sensitive imaging modality for detecting ILC, with an overall sensitivity of approximately 93%. Unlike mammography and US, MRI provides functional imaging by assessing tumour vascularity and enhancement patterns. ILC most commonly appears as an irregular, spiculated mass on MRI but can also present as non-mass enhancement, making it particularly useful for identifying multifocal or contralateral disease.
Abbreviated breast MRI (AB-MRI) has emerged as a promising alternative to standard MRI, offering comparable sensitivity with reduced imaging time and cost. However, one limitation of MRI for ILC detection is its reliance on contrast enhancement, as ILC tends to exhibit delayed rather than rapid enhancement compared to IDC. Emerging imaging modalities, such as contrast-enhanced mammography (CEM) and artificial intelligence (AI)-assisted imaging, are being explored to improve ILC detection further. Early studies suggest that CEM offers better sensitivity than DM and DBT, with specificity comparable to MRI. Additionally, AI-based radiomics and deep learning tools have shown potential to enhance the identification of ILC by improving radiologist confidence and detection accuracy.
Invasive lobular carcinoma presents significant challenges in breast cancer screening due to its unique histologic characteristics and subtle imaging findings. While mammography remains the standard screening tool, its limitations in detecting ILC necessitate the use of supplemental imaging modalities. Digital breast tomosynthesis has improved detection rates, particularly in dense breasts, while ultrasound provides an additional means of identifying mammographically occult ILCs. MRI remains the most sensitive modality, particularly for evaluating multifocal or contralateral disease. As imaging technology advances, emerging modalities such as CEM, AB-MRI and AI-assisted detection hold promise for improving ILC detection and ensuring earlier diagnosis and better patient outcomes. Continued research is needed to refine screening protocols and develop risk-based approaches tailored to the unique detection challenges of ILC.
Source: Journal of Breast Imaging
Image Credit: iStock
