Invasive Lobular Carcinoma (ILC) is the second most frequently diagnosed type of breast cancer, representing 10% to 15% of all invasive breast cancer cases. ILC has a unique biology and growth pattern compared to the more common ductal carcinoma, which affects its diagnosis, treatment response, and overall prognosis. Understanding the survival outlook for ILC requires considering the cancer’s stage at diagnosis, its specific biological characteristics, and the effectiveness of modern treatment strategies.
Understanding Invasive Lobular Carcinoma
Invasive Lobular Carcinoma begins in the lobules (milk-producing glands), unlike Invasive Ductal Carcinoma (IDC), which originates in the milk ducts. A defining feature of ILC is its characteristic growth pattern: cancer cells move in single-file lines or thin strands rather than clumping together to form a solid mass.
This diffuse growth pattern makes ILC challenging to detect with standard mammography, sometimes resulting in a later diagnosis or a larger tumor size compared to IDC. Biologically, ILC involves the loss of the E-cadherin protein, which is necessary for cell-to-cell adhesion. This loss explains the non-cohesive, single-file cellular arrangement that is the hallmark of the disease. ILC is overwhelmingly hormone receptor-positive (possessing ER and/or PR), which strongly influences treatment selection and long-term outlook.
ILC Survival Rates Based on Disease Stage
Survival statistics are typically expressed as a 5-year or 10-year relative survival rate, estimating the percentage of people with ILC expected to be alive compared to the general population. These statistics depend heavily on how far the cancer has spread at diagnosis, categorized by registries like the Surveillance, Epidemiology, and End Results (SEER) Program.
For cancer confined to the breast, categorized as Localized disease, the survival rate is very high, comparable to the overall localized breast cancer rate of about 99%. When the cancer has spread to nearby structures, such as the lymph nodes in the armpit, it is classified as Regional disease. The 10-year relative survival rate for ILC with regional spread is approximately 76%.
The survival outlook shifts when the cancer has metastasized, or spread to distant organs, categorized as Distant stage disease. For this stage, the 10-year relative survival rate for ILC is approximately 12%. While ILC often has a slightly better prognosis than IDC initially, some studies show the long-term survival rate for regional or distant ILC can be slightly lower than IDC, possibly due to its tendency for later recurrence. The overall 5-year and 10-year relative survival rates for ILC across all stages are reported to be around 88.6% and 73.6%, respectively.
Biological and Patient Factors Affecting Prognosis
While stage is the most significant indicator of prognosis, individual outcomes are also determined by the tumor’s specific biology and patient-related variables. The vast majority of ILC tumors are hormone receptor-positive, a favorable characteristic because it makes the cancer susceptible to endocrine therapy. The tumor’s grade, which describes how abnormal the cancer cells look under a microscope, also plays a role.
ILC is often a lower-grade cancer, meaning the cells are slower-growing and look more like normal cells. The proliferation rate, measured by the Ki-67 index, indicates how quickly the cancer cells are dividing; a lower Ki-67 score is associated with a better prognosis. The status of the lymph nodes is another significant factor, as the presence and number of positive lymph nodes strongly indicate the likelihood of distant spread. Patient factors, such as age at diagnosis and co-existing health conditions, influence the ability to tolerate aggressive treatments and recover.
Treatment Strategies and Their Influence on Outcome
The standard treatment approach for ILC involves a combination of local and systemic therapies, which directly impact survival rates. Local treatments include surgery, often followed by radiation therapy to reduce the risk of cancer returning in the breast or chest wall. Systemic therapies are administered to kill cancer cells throughout the body and are important for improving long-term outcomes.
Due to the high frequency of hormone receptor-positivity in ILC, Endocrine Therapy is the cornerstone of systemic treatment for most patients. These medications, such as tamoxifen or aromatase inhibitors, block the effects of estrogen or lower estrogen levels, starving the cancer cells and significantly reducing the risk of recurrence.
ILC is often a lower-grade, slower-proliferating cancer, making it generally less sensitive to chemotherapy compared to many IDC tumors. Therefore, chemotherapy is not universally required for all ILC patients. The long-term use of endocrine therapy, often for five to ten years, is a primary driver in the high survival rates for early-stage ILC, mitigating the risk of late recurrence characteristic of this cancer type.