Graced with good weather and even better science, the 2026 International Invasive Lobular Carcinoma (ILC) Symposium, held September 23-25 in San Francisco, marked a decade of focused research on long understudied lobular breast cancer.
It’s the second most common subtype and just as prevalent as ovarian or liver cancer, but many patients (including those diagnosed with it) have never heard of lobular and don’t realize it behaves differently than ductal, the most common breast cancer type. First identified in 1941 as “round cells that don’t stick together and infiltrate the tissue in single file,” lobular research remained scattered for decades.
But in 2016, the first International ILC Symposium gathered to flip that script, creating an ambitious research agenda and forging partnerships among researchers, clinicians and patient advocates worldwide that have resulted in new discoveries, bold initiatives and an impressive spike in ILC research fundraising. There’s even a lobular research roadmap now.
“The advocate voice is essential,” said surgical oncologist and symposium chair Rita Mukhtar, MD, head of the UCSF Lobular Breast Cancer Program, in her opening remarks. “Not just for fundraising, but for research. It was a lobular patient who inspired the PLUMB Registry, which is tracking tumor response to therapy by measuring ctDNA, so lobular patients with unmeasurable disease can be in clinical trials.”
Ten years later, attendees celebrated the progress in ILC awareness and research, while also acknowledging the unanswered questions that remain, the tailored treatments still in the offing and the fact that lobular, according to statistics, is once again on the rise.
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‘Patients with lobular are like a square peg being pounded into a round hole, with no option but to follow treatment protocols for other breast cancers.’
― Leigh Pate, patient advocate and founder of the Lobular Breast Cancer Alliance
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“There have been a lot of positive changes, no question,” said University of Pittsburgh molecular biologist Steffi Oesterreich, PhD, of the symposium’s 10-year history. Among those accomplishments: the creation of ILC datasets with multi-omics data; the integration of ILC research into major conferences; a better understanding of ILC’s microenvironment; advances in imaging and pathology; the launch of several ILC clinical trials and new ILC models courtesy of the patient-derived organoid biobank, the BCRF ILC Legacy Project.
“I hope I’ve gotten that progress across, but there are still gaps,” she said, summoning her inner devil’s advocate. “There’s still limited progress with regard to our ultimate goal: precision medicine for patients with ILC. We still have no molecular marker to tell us whether patients should have chemo or not. We still have no change in treatment.”
Oesterreich borrowed a call to action from Leigh Pate, a Fred Hutch Cancer Center patient advocate and devoted cyclist who along with others, including Oesterreich, founded the Lobular Breast Cancer Alliance in 2017 and, upon her death in 2022, endowed the Breast Cancer Research Foundation (BCRF) with funding to launch the ILC Legacy Project.
“As Leigh would say, we need to ‘keep pedaling’ and keep pushing,” Oesterreich told the gathering. “Don’t settle for the status quo. We still need dedicated funding mechanisms and more fundamental research of basic ILC biology. We still need to push pharma to support ILC trials.”
Loss of e-cadherin, a cellular “glue” encoded by the CDH1 gene, is the defining molecular hallmark of ILC. That’s what creates its signature single-file growth pattern; instead of making lumps, lobular tends to grow in lines, strands and sheets, producing tucks or dents or dimples or thickened skin.
For the public and primary care providers (PCPs), this means ILC is harder to find on physical exams and harder to see with mammograms, especially in dense breast tissue.
For patients, this means being diagnosed at a later stage (sometimes after years of clear mammograms) when the cancer’s harder to cure. It can also mean not being eligible for clinical trials because they usually require measurable disease in order to track a therapy’s efficacy and lobular is notoriously hard to measure. Surveillance and survivorship can be trickier, too.
Over the course of three days, the gathered global lobular community ― or “glob mob” ― hammered home these unique features: ILC’s diffuse growth pattern; its unconventional metastatic sites (the gastrointestinal and gynecologic tracts, peritoneum, meninges, etc.); its distinctive immunological and molecular profile; its uneven response to chemotherapy and positive response to radiation as well as to P13 mutations and immune targets, which are more common in ILC than IDC.
Patient advocates, too, shared lived experiences of lobular: deceptively clear mammograms, inaccurately staged cancers, dismissed symptoms due to “invisible” disease, metastatic recurrences decades post-treatment, and hospitalizations from ILC bowel obstructions.
Yet in clinics across the U.S., lobular is still thought of ― and treated ― just like other estrogen-receptor-positive breast cancers. There are no specific ILC treatments.
But there is momentum. The symposium has tripled in size over the years, with more than 300 participants traveling from across Europe, the U.S., the UK, Australia, New Zealand and beyond, some with big news to share.
There are now a half dozen lobular clinical and research programs at major U.S. cancer centers like Dana-Farber, Memorial Sloan Kettering, UCSF and the University of Colorado, and a new research collaboration, the Lobular American Research Consortium (LARC), was just launched with seed money from the lobular nonprofit Dynami Foundation.
“We now have 18 independent research teams to address these major clinical and research questions,” said LARC co-chair, molecular biologist Matthew Sikora, PhD, of the University of Colorado. “This is about collaboration, not competition, and we hope to fully engage patient advocates with our research projects.”
Fred Hutch will join the growing group, per breast oncologist Hannah Linden, MD.
“Our group, led by Dr. Heather Parsons, is in support of us joining LARC, and will bring the expertise of our basic and translational breast cancer research team including Drs. Cheung, Davidson and Velimirovic,” she said. “It’s a great opportunity for us to collaborate with other centers. Leigh Pate helped us connect with Steffi and Rita and her spirit will help drive us to work with the international group to better understand and treat ILC.” Parsons holds the Maudslien Endowed Chair in Breast Cancer Precision Oncology Research
The LBCA, which raises both research funds and awareness for ILC, announced a new $1 million donation that will power two $500,000 research grants; they also launched a cross-country “rolling billboard” bus tour aimed at increasing the “alarmingly low” awareness of ILC― not only in patients, but in medical providers, one reason they’ve created a series of CME-accredited education webinars for clinicians, PCPs, OB-GYNs and others.
Belgium researcher Karen Van Baelen, MD, PhD, presented on ways to reduce the risk of lobular, pointing to several modifiable factors including BMI, diet and physical activity, smoking, alcohol intake, stress and pharmaceutical hormones.
“My take home message is that physical activity consistently improves breast cancer outcomes,” she said, adding that smoking cessation also shows a survival benefit. Systemic pharmaceutical hormones, however, are “not a good idea,” since ILC is highly sensitive to hormones.
Previous research by Fred Hutch’s Chris Li, MD, PhD, in fact, found that combined hormone therapy increased the risk of lobular fourfold after just three years of use. Li holds the Helen G. Edson Endowed Chair for Breast Cancer Research.
Coffee, Van Baelen added, appears to have a slight protective effect, prompting cheers from the audience.
As for screening, experts said digital breast tomosynthesis detects lobular better than standard 2D mammography, but neither are as sensitive as contrast-enhanced MRI, which was approved in 2011 and is more accessible, more affordable and uses less of the contrast agent gadolinium.
Whole-body diffusion-weighted MRI (WB-DWI/MRI), however, was touted as the best imaging modality for lobular. The only problem is its accessibility. WB-DWI/MRI’s technology is cleared by the U.S. Food and Drug Administration, but not its use as a screening tool, so it’s not covered by insurance in the U.S.
A retrospective study of nearly 100 patients with ILC who received scans via WB-DWI/MRI found that it “outperformed conventional staging in the detection of distant metastases,” calling it a “clinically efficient one-stop-shop examination” for ILC patients. The DELILA trial, launching soon in Belgium, will evaluate its use in metastatic patients.
During an imaging panel sponsored by SNMMI, the Society of Nuclear Medicine and Molecular Imaging, Linden, who holds the Athena Distinguished Professorship of Breast Cancer Research at UW Medicine, spoke about the PET scan tracers FDG and FES in staging metastatic ILC. Linden and colleagues were instrumental in developing FES, the estrogen-based imaging agent and she just published another study underscoring its value in diagnosing, staging, restaging and managing ER+ cancer.
“ILC is challenging, but it can be imaged,” she said. “FES PET isn’t perfect, but it’s helpful in ILC. It frequently shows a greater extent of disease and is well visualized in bone, breast, lymph nodes, lung, brain, uterus and ovaries.”
FES is not as adept at picking up met sites in the liver and peritoneal cavity, she said. It also does not pick up ER-negative tumors or cells. Linden called FES and FDG PET complementary tools, as both are helpful to assess the extent of metastasis. But biopsies remain the gold standard.
“They pick up all the molecular targets, and you need the active mutations and personalized targets,” she said. “But FES can show you where to put the needle.”
Also on the horizon is FAPI (fibroblast activation protein inhibitor), another new PET tracer that targets cancer-associated fibroblasts (CAFs), part of the tumor microenvironment. David Mankoff, MD, PhD, formerly of Fred Hutch/University of Washington and now at University of Pennsylvania, noted that FAPI, as well as PARPi tracers and theranostics (aka “liquid radiation”) may hold promise for ILC, as well.
Patient advocate Gretel Roberts, PhD, of Auckland, New Zealand, presented a poster on the use of a FAPI PET/CT in her own ILC. Initially diagnosed with and unsuccessfully treated for stage 2 ILC, she underwent a FAPI scan which found “extensive metastatic cancer” missed on her initial bone scan and CT. Armed with an accurate stage 4 diagnosis, she was then treated with trastuzumab deruxtecan, or T-DXd, which controlled her disease.
“Unless you’re bold, it’s hard to make progress,” advised keynote speaker Laura Esserman, MD, MBA, best known for her innovative I-SPY breast cancer trials. Esserman called lobular a “misunderstood entity” and went on to talk about the importance of smart clinical trial design.
“A trial is an engine,” she said. “You need to keep it running. Cast a big net to get lots and lots of people on. And make sure no piece of information is lost or wasted.”
Rachel Jankowitz, MD, director of the Rena Rowan Breast Center the University of Pennsylvania and LARC co-chair, talked about ILC incidence in premenopausal patients, which is rising.
“It’s clearly not a disease of older patients,” she said. “In a UCSF cohort of 800 ILC patients, 28% were premenopausal and in a Penn cohort, 35% were premenopausal.”
Others shared insights on Diffuse Gastric and Lobular Breast Cancer Syndrome (driven by a pathogenic CHD1 variant); ILC’s immunogenic profile (it’s mixed!) and the potential, or lack thereof, for using liquid biopsy in lobular.
“Patients with purely peritoneal or pleural-based disease are effectively contained to those spaces,” said Linden. “They are among the groups who don’t seem to shed into blood. So while liquid assays are promising it’s like many other situations; they may not be effective in all cases.”
Overall, Linden called the meeting “very promising.”
“We have huge advances for ER+ tumors, and PI3K mutation-bearing tumors and many of the patients in these trials have ILC,” she said. “We are making incremental progress, but alas no one test or treatment is perfect.”
Lobular researchers “keep pedaling,” though.
Pathologist Patrick Derksen, PhD, from the University Medical Center in Utrecht, The Netherlands, spoke about the promise of AKT inhibition for ILC therapy. A clinical trial aimed at high-risk lobular patients is currently investigating AKT inhibition via capivasertib.
“We think this is a potential intervention in lobular,” he said. “We don’t understand the pathway entirely but clearly, there’s synergy.”
Sikora brought up another potential treatment route, PARP inhibition.
“ILCs carry distinct features of dysfunctional DNA repair,” he said. “They don’t show HRD features so patients are ineligible for PARP inhibition, but we’ve seen durable response to PARP inhibition in vivo [within living tissue].”
Fred Hutch translational researcher Kevin Cheung, MD, PhD, spoke on lobular’s metastatic spread via tumor cell clusters, “mini-ecosystems” that allow single cells to team up to survive, spread and grow. These clusters are more prevalent in ILC than in ductal breast cancer.
“Tumor cell clusters are efficient metastasizers that produce locally confined growth signals that collectively promote metastasis,” he said.
A clinical researcher and oncologist, Cheung is currently studying this intercellular communication, trying to “fish out” the talkative proteins in order to study and, ultimately, stop them from wreaking havoc. In experiments with ILC cells, he said he can see the result of this intercellular crosstalk: rapid tumor growth.
Cheung, who’s treated patients with lobular, said he’s seen this process unfold in the clinic and is currently collaborating with the Sikora Lab to find a way to shut it down.
“We don’t know what the signal is yet,” he said, channeling a bit of that boldness Esserman mentioned. “But Matt Sikora and I are going to find it.”
Diane Mapes is a senior editor and writer at Fred Hutch Cancer Center, who's written for NBC News, TODAY, CNN, MSN, Seattle Magazine and other publications. A breast cancer survivor and patient advocate, you can reach her at dmapes@fredhutch.org or doublewhammied.com / @double_whammied / @doublewhammied.bsky.social. Just diagnosed and need information and resources? Visit our Patient Care page.
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