What Is Invasive Lobular Breast Cancer? The Type That Doesn’t Always Make a Lump

Breast Cancer

29 Sept

Most breast cancers grow like a marble in a sponge. Lobular grows like a cobweb through it.

You've got a piece of paper in front of you, and somewhere on it are the words invasive lobular carcinoma. Or maybe somebody said "lobular" in clinic. Or maybe you're the woman who could feel that something in her breast had changed, and the mammogram came back clear, and it took another round of scans before anybody used that word at all.

What you want to know is whether lobular is worse. It's the first thing everyone wants to know, and nobody says it out loud. So let me tell you where the difference comes from. It isn't a different disease living in a different place. It's one missing protein — E-cadherin — and every strange thing about lobular comes out of that one thing.

Watch the video

What Is Invasive Lobular Breast Cancer? The Type That Doesn't Always Make a Lump

This post is the written version of my video. I'm a breast surgeon; I do these operations and explain these reports, and lobular is the one I spend longest explaining in clinic.

Watch on YouTube →

One missing protein

Lobular breast cancer is a cancer whose cells have lost the thing that makes them stick to each other. That's the whole difference. Everything else follows from it.

The thing they've lost is E-cadherin, a protein on the surface of a breast cell that holds it to the cell next door — the glue between the bricks, rather than the bricks themselves. Most breast cancers keep it. In lobular, it's gone or not working. And a cell with no glue doesn't pile up into a ball. It slips off on its own and travels through the tissue in single file, threading between the normal structures rather than pushing them out of the way. That's the cobweb.

It's also more common than many women think. Lobular is the second most common type of breast cancer: 10–15% of all breast cancers, and rising. In the United States that's around 43,000 women a year (Lobular Breast Cancer Alliance). There's a large, well-organised community of women with lobular who've said for years that it gets treated as a footnote. They're right about the footnote. They're wrong that it means nobody knows anything about it — we know a great deal.

Classic or pleomorphic. Most lobular cancer is the classic type. A less common type, pleomorphic — under 5% of lobular cancers — has cells that look more abnormal under the microscope and tends to behave more aggressively. If your report says pleomorphic, ask your team what that changes for you. If it doesn't, yours is almost certainly classic, and you can stop reading about the other one at two in the morning.

LCIS isn't the same thing. Lobular carcinoma in situ — LCIS — is not a cancer. It's a marker that your breast tissue has a higher-than-average chance of developing a cancer at some point, in either breast, and it usually means closer follow-up, such as yearly mammograms. Invasive lobular carcinoma is a cancer, and it's what this post is about. If your report says invasive, that's the word that matters. If it says LCIS on its own, with no invasive cancer anywhere in the report, you're in a different conversation.

Why your mammogram might have been clear

Here's the thing about a cobweb: often, you can't feel one.

A ductal cancer makes a lump because the cells stick together and build something with edges. You can feel edges. I can feel edges. A mammogram can see edges. Lobular often doesn't do that. Sometimes it does — I've had a woman whose lobular cancer was a tiny two-millimetre lump, and plenty of women find an ordinary lump. But often what it makes instead is a thickening: an area that feels firmer, fuller, or like the tissue has more resistance in it, with no border to trace. Women describe a ridge, a shelf, a patch that's gone denser, or one side that doesn't feel like the other any more.

And some of it you see rather than feel. A dimple or pucker in the skin when you lift your arms or press your hands together. Skin that's gone thicker or harder. A nipple that has pulled in when it never used to. Occasionally, one breast getting smaller, because lobular can pull the tissue in as it grows. If you've quietly noticed your bra fitting differently on one side, say it out loud to your doctor.

On a mammogram, a diffuse thing without edges is hard to see. There's often no mass, and often none of the little calcium specks that make radiologists look twice. Sometimes the only sign is that one breast has quietly got denser than the other over a few years — which you can only spot by comparing mammograms over time.

So screening picks up lobular less reliably than ductal. That isn't carelessness; it's a well-described limit of the test in this type of cancer. In the densest breast tissue — density D — a mammogram's ability to pick up lobular has been reported as low as 11% (Lobular Breast Cancer Alliance).

What that number doesn't tell you: it's the worst end of the range, in the densest breasts, and only about 1 in 10 women have density D. In fattier breasts a mammogram does considerably better, and 3D mammography does better than the older 2D. The version online — that mammograms can't detect lobular at all — isn't true. They can, and they do, much of the time. They miss it more often than ductal, and most often in the women who are hardest to image anyway.

A clear mammogram is an answer about your breast on the day of the mammogram. It isn't a permanent certificate, and it doesn't overrule your own hand. If you can feel a change, a clear mammogram doesn't close the question — it means the mammogram didn't show anything, which is a different sentence. If the thing you can feel is still there in a few weeks, it needs looking at again, with something other than a mammogram. You're allowed to go back and ask for more imaging or a specialist referral.

Women with lobular tell me, over and over, that they knew something had changed, and they were reassured, and they accepted it because it came from a scan and their own hand felt like a lesser instrument. It isn't. It's the one instrument that's on you every day.

Why they keep sending you for more scans

Because a mammogram often can't tell us how far the cobweb goes. The extra scans aren't bad news. They're us trying to find the edges of something that doesn't have obvious edges, before we take you to theatre.

An ultrasound usually comes next. It's better at lobular than a mammogram, though it can still under-read how much tissue is involved. Then, in many units, we'll ask for an MRI or a contrast-enhanced mammogram — the most sensitive ways we have of seeing lobular inside the breast. They pick up more. That's the point.

In my practice, I use MRI or contrast-enhanced mammography for every woman diagnosed with lobular cancer, and most surgeons in Wellington do too. Practice varies across New Zealand, mostly depending on access to those scans. The downside of MRI is that it's very sensitive but less specific: it lights up things that turn out to be nothing, which can mean a biopsy that comes back benign — and a fortnight spent worrying for no reason.

Something that surprises people: there are no separate imaging guidelines for lobular breast cancer. Not for screening, not for measuring its extent before surgery, not for follow-up. The guidelines were built on breast cancer as a whole — in practice, mostly ductal — and lobular was carried along inside them. That's a gap in the evidence, and it's why practice varies so much between units and countries.

Where you live changes this

If you're in the US, the UK or Australia, you may be offered different imaging from what I'd offer in Wellington — and neither of us is doing it wrong. With lobular, practice is personalised — and, in this case, under-standardised.

The second operation. The consequence that upsets most women: lobular is often bigger on the final pathology than it looked on the scans. So it's more common that we remove what we planned to, and the report comes back saying the cancer reached, or came close to, the edge — and you need a second operation to take a bit more. In the largest analysis, of more than 87,000 women, lobular came back with involved margins about 36% of the time, against about 13.5% for ductal (O'Connor et al., 2021). Roughly one in three, against one in seven.

If that's happened to you, nobody made a mistake. Your surgeon didn't cut in the wrong place and the radiologist didn't miss it. We aimed at the edges of something that fades out rather than stops, and the fading-out part doesn't show on a scan. It's worth being told about beforehand, not after.

What your own report actually says

Find the receptor line. It's the one that decides most of what happens next: oestrogen receptor (ER), progesterone receptor (PR), and a protein called HER2. In lobular cancer they nearly always fall the same way — ER positive, PR positive, HER2 negative. Not always; sometimes PR is negative or HER2 is positive. But it's one of the most consistent things about lobular there is.

Oestrogen receptor positive means the cancer cells have kept the receptor that oestrogen fits into, so oestrogen is part of what drives their growth. That sounds alarming, and it's the opposite. A cancer that runs on something is a cancer we can treat by blocking it. That's the whole basis of hormone tablets — tamoxifen and the aromatase inhibitors — and in lobular they often do the most work, over the longest time. HER2 negative means the cancer isn't driven by that protein, so HER2 drugs like Herceptin aren't for you. That's not a loss. It's a different route.

The one that confuses people is grade. Lobular is usually grade 1 or 2, meaning the cells look more like normal breast cells and divide more slowly — fewer than 1 in 10 classic lobular cancers are grade 3 (Quirke et al., 2024). Yet lobular is often larger when we find it. Those don't contradict each other. Grade is how the cells behave — their personality. Size is how long the cancer was there before anyone found it. A slow cancer that was hard to see for two years can be large and low grade, and that combination sounds very much like lobular.

There may be a fourth number, Ki-67, written as a percentage: how many cells were actively dividing when the sample was taken. Lower generally means slower. It's useful, but a slightly unreliable number.

Does chemotherapy work on lobular?

Chemotherapy works differently on lobular. Somewhere on the internet, "differently" has become "not at all", and that isn't what the evidence says.

Here's where the belief comes from. When chemotherapy is given before surgery, we measure how well it worked by whether any cancer is left at the operation — "nothing left" is called a complete pathological response. In the same large analysis of more than 87,000 women, lobular reached a complete response about 7% of the time, against about 22% for ductal (O'Connor et al., 2021). Roughly one in fourteen, against one in five. That's a big difference.

But look at what it measures: whether the cancer vanished completely during three to six months of chemotherapy. Chemotherapy works best on fast-dividing cells, and lobular is usually slow-growing and hormone-driven. A cancer that was never dividing fast was never likely to vanish in a few months. What that finding changed was the order: if chemotherapy is unlikely to shrink the cancer enough to allow breast-conserving surgery, giving it first may not buy you anything. So in many units, women with lobular go to surgery first, and any chemotherapy comes after.

Over the last ten years, the timing of chemotherapy for lobular in Wellington has changed a lot. We now use it very rarely before surgery, and less often even after it. So the question to ask isn't "does chemotherapy work on lobular?" It's: is it being recommended for me, what is it expected to add, and should it come before or after my surgery?

Which hormone tablet, and why it matters

If one thing in this post is specific to lobular rather than breast cancer in general, it's this.

Almost all lobular cancer is oestrogen positive, so almost every woman with it will be offered a hormone tablet for five or ten years. There are two families: tamoxifen, which blocks the oestrogen receptor, and the aromatase inhibitors — letrozole, anastrozole, exemestane — which block the enzyme that makes oestrogen in the body after menopause.

For a long time the choice was made on general breast cancer evidence. Then the BIG 1-98 trial looked at lobular and ductal cancer separately, in nearly 3,000 women whose pathology was centrally reviewed, followed for a median of about 8 years. In lobular cancer, letrozole compared with tamoxifen reduced the risk of the cancer coming back, or of dying, by 50% in the slower-growing group and 66% in the faster-growing group. In ductal cancer, the same comparison gave a 35% reduction in the faster-growing group and no meaningful difference in the slower one (Metzger Filho et al., 2015). Same trial, same two drugs — a much bigger difference for lobular.

What that doesn't say: that tamoxifen is useless in lobular. That's the version circulating online, and it isn't what the trial found. And an aromatase inhibitor only works properly after menopause. If you're premenopausal or perimenopausal, it has to be paired with treatment that switches the ovaries off, which brings its own problems.

The two feel different, too. Tamoxifen tends towards hot flushes, with a small raised risk of blood clots and changes to the lining of the womb. Aromatase inhibitors tend towards joint pain and stiffness, and they thin the bones, which is why we usually offer a bone density scan. Neither is a reason to refuse the tablet. Both are a reason to speak up early if you're struggling — the tablet only works if you take it, and the commonest reason women stop is a side effect nobody adjusted for. In my practice I tailor the choice to the side effects too, but aromatase inhibitors are used more in lobular.

The other breast, and whether you need a double mastectomy

Two different things get told together here, and separating them matters, because the muddle sends women into operations they may not need.

The first is more than one area in the same breast. That is more common in lobular — the cobweb again — and it's part of why the scans matter.

The second is the other breast, and the number doesn't support the way this gets said. You'll read that lobular is "usually" or "often" in both breasts. The risk of a cancer developing in the other breast is under 8% over 20 years — low, and not very different from ductal (Lobular Breast Cancer Alliance). The limit on that: it's a long-term estimate drawn from many women, not a prediction for you, and a strong family history or a known gene fault can change it.

In my practice, I don't offer a double mastectomy for lobular unless there's cancer or atypical cells on imaging and biopsy on both sides. Lobular on its own doesn't mean you need both breasts removed. Multiple studies support breast-conserving surgery with radiotherapy as a safe option for lobular, with survival no different from removing the whole breast. What is true is that keeping the breast sometimes isn't possible — if the cancer is in more than one place, or the margins keep coming back involved. Then a mastectomy may be the sensible operation. But that comes from your scans and your pathology, not from the word "lobular".

Which operation to have is your decision. It depends on where the cancer is, how much breast you have, what the scans show, what you want, and what you can live with afterwards. Make it a conversation rather than a verdict: ask what the alternatives are and why each was ruled in or out for you. Ask whether keeping the breast is on the table — and if not, exactly what would have to change for it to be.

Second opinions are normal and appropriate — and you have time.

A breast cancer diagnosis is frightening, and it's almost never a medical emergency in the sense of needing a decision this week.

Is lobular worse, and where does it go?

Stage for stage, women with lobular tend to do at least as well as women with ductal, often slightly better, because lobular is usually lower grade and hormone positive — both favourable.

After about eight years, the picture is less simple. Lobular tends to come back later rather than earlier, if it comes back. And where it goes can differ: to the same common places as any breast cancer — bones, lungs, liver — but also, more than ductal does, to some unusual ones: the lining of the abdomen, the stomach, the bowel, the ovaries, the skin. Those are harder to spot because the symptoms are vague and easy to put down to something else.

What that doesn't mean: that lobular usually goes to the gut. It means it can, and most women reading this will never need to know any of it. It's here because those are the symptoms women don't report.

Most of what we know about breast cancer treatment came from trials where lobular was a small minority, with results reported for everyone together. So what I can tell you about lobular at 15 years comes from smaller, messier evidence than the equivalent for ductal, and trials designed specifically for lobular are only now being built. I don't know exactly what your lobular cancer will do at fifteen years. Nobody does. That's an argument for taking the hormone tablets seriously and staying connected to your team for the long haul — not an argument for being frightened. A cancer whose main risk comes later is one where the tablets you take for years are doing more of the work than chemotherapy ever would.

What to do if something changes

Most of what you notice during treatment is from the treatment, not the cancer. But a few things mean don't wait, and I'll sort them by how fast to act.

The emergency department, now: a temperature, or shivering, while you're having chemotherapy — especially if you feel properly unwell in yourself. You'll have a card and a number for exactly this. It's the one thing in cancer treatment that doesn't wait until morning.

When you ring or arrive, say:

"I'm having chemotherapy and I have a temperature."

That sentence puts you in a different queue from "I just feel unwell". It tells the person in front of you this could be neutropenic sepsis, and that changes what happens in minutes rather than hours.

A phone call today, not tomorrow: a surgical wound that's getting redder, hotter or more painful rather than less, or leaking fluid; new breathlessness; or a new area of thickening in either breast that's appeared and stayed.

A call in the next few days: something you can feel that's different from last month and hasn't settled; persistent bloating or a change in bowel habit that's gone on for weeks with no explanation — I include this because of how lobular can spread, and because women put it down to treatment and don't mention it; or bone pain in one spot, at rest and at night, lasting two weeks or more.

The thought that will stop you ringing: "I had a scan last month, they'd have seen it." That scan answered a question about that day. If something has changed since, it needs looking at again, and nobody on your team will think you're being difficult. With lobular in particular, the thing you can feel may not be the thing the scan showed.

Once a month, on the same date, have a proper look and feel of both breasts and both armpits, in the same place and the same light. You're not hunting for a lump. You're looking for a difference from last month. Write down the date and one line about what you found, even if it was nothing. That line is worth more at your next appointment than anything you'll read online.

Did somebody miss this?

When a woman with lobular sits down in my clinic, the question underneath the other questions is usually some version of: how long has this been here, and did somebody miss it?

Sometimes the answer is that a mammogram was clear three months ago and the cancer was probably already there. I won't pretend otherwise. It happens with lobular, for exactly the reasons above. But being missed by a test isn't the same as being let down by a person. A mammogram that doesn't show a cobweb is a test doing what the test does. The failure, if you want to call it that, is in the tool — and in the fact that we've never built a screening programme around this type of cancer.

And the other half, the one that keeps women awake: should I have found it sooner? No. You were feeling for a lump, because that's what every leaflet has told you to feel for, and lobular often doesn't make one. You were doing it right; the instruction was incomplete. The better instruction — the one I give my own family — is to check for a difference from last month, not for a marble.

If you're wondering whether your daughter should be screened differently: if there's a strong family history, that's a conversation with your genetics service. Ask your team whether you meet the criteria where you live.

Five things to find on your report tonight

Invasive or in situ? Invasive lobular carcinoma, or lobular carcinoma in situ (LCIS). Different words, different situations.
Classic or pleomorphic?
The size, in millimetres.
The receptors: oestrogen, progesterone and HER2.
The grade — 1, 2 or 3 — and the Ki-67 percentage, if there is one.

Those five are most of what decides the plan. Once you've written them down, you're not borrowing anyone else's answer any more.

Then take two questions to your next appointment:

"Given this is lobular, what imaging are we using to work out how big it is — and is an MRI part of that?"

"Given this is lobular, which hormone tablet are we choosing, and why that one?"

The second is the one almost nobody asks, and the one where lobular rather than ductal may change the answer.

Because it's the cobweb, not the marble. That's why it's hard to feel, why the mammogram can be clear, why the scans keep coming, why the size changes and why a second operation isn't a mistake. One missing protein, and everything downstream of it.

You have time. Ask the question. Then make the decision yourself.

The video

What Is Invasive Lobular Breast Cancer? The Type That Doesn't Always Make a Lump

All ten chapters — the cobweb, the scans, your report, chemotherapy, the tablets and the other breast — if you'd rather watch, or want to send it to someone who's just been told.