Breast Care A-Z · Condition · ILC

Invasive lobular carcinoma

also: ILC, infiltrating lobular carcinoma, lobular breast cancer

Invasive lobular carcinoma (ILC) is the second most common type of breast cancer; it begins in the milk-producing lobules and tends to spread in single-file strands, which can make it harder to feel and to see on a mammogram. You may have been told your biopsy shows lobular cancer, or be reading about how it differs from the commoner ductal type.

Quick answers

Is lobular cancer worse than ductal cancer?

On average, no. Lobular and ductal cancers have broadly similar outcomes when matched for size, grade, and other features. The differences are in how the cancer is investigated and surgically planned, not in long-term survival.

Why am I being sent for an MRI?

Lobular cancer is sometimes more extensive than mammogram and ultrasound suggest, because the diffuse growth pattern can be subtle on those tests. MRI gives a more complete map of the cancer and can change the surgical plan — for example, identifying a second area in the same breast or in the other breast that needs assessment before surgery.

Is lobular cancer more likely to come back?

Recurrence depends on size, grade, lymph node status, and treatment, not on the lobular versus ductal label per se. Where there is a difference, lobular cancers tend to recur later than ductal cancers — sometimes 10 years or more after treatment — which is one reason long-term hormone therapy is often recommended.

BREASTORY ENCYCLOPEDIA · PLATE LVIII ONCOLOGY · INVASIVE BREAST CANCER invasive lobular carcinoma ILC · infiltrating lobular carcinoma the second most common breast cancer, arising from lobular epithelium with characteristic single-file infiltration and frequent mammographic occultness i FIG 01 ILC Histological Pattern · Indian File Infiltration Normal lobule (E-cadherin intact) v · TDLU origin E-cadherin intact → ILC i · Single-file (Indian file) infiltration ii · Discohesive cells (E-cadherin lost) iii · Targetoid / periductal pattern iv · Stromal fibrosis without discrete mass Callouts: i=Indian file infiltration ii=discohesive cells (CDH1 loss) iii=targetoid pattern iv=stromal fibrosis v=TDLU origin Why Mammography Is Challenging ILC infiltrates without displacing tissue No mass · no spiculation · no desmoplasia Architectural distortion only on mammogram MRI sensitivity >85% for ILC vs ~65% for mammography alone Receptor Profile >90% ER-positive · >90% PR-positive HER2-negative (rare <5% HER2+) CDH1 gene (E-cadherin) loss · hallmark Low-to-intermediate grade (G1–G2) typically Exception: pleomorphic ILC (grade 3) ii FIG 02 ILC vs IDC · Clinicopathological Comparison Feature ILC (~15%) IDC (~80%) Growth pattern Diffuse, infiltrative Mass-forming, spiculated Mammographic Often occult (architectural distortion) Spiculated mass E-cadherin Lost (CDH1 mutation) Preserved ER status >90% ER+ ~75% ER+ HER2 Rare (<5%) ~20% Grade Often grade 1–2 Variable Bilaterality 10–15% <5% Metastatic sites Peritoneum, GI, meninges, ovary Lung, liver, bone BCS Possible, higher re-excision Standard option iii FIG 03 ILC Subtypes · Patterns and Prognosis Subtype Pattern Prognosis Classic ILC Single file, small cells Intermediate Solid ILC Sheets of cells Worse Alveolar ILC Groups of 20+ cells Intermediate Mixed ILC Combined patterns Variable Pleomorphic ILC Large pleomorphic cells Worse (grade 3) Tubulolobular Tubule formation + lobular Better Signet ring cell Mucin-filled cells Variable With LCIS Associated lobular neoplasia Relevant for margins E-cad+ (unusual) Rare variant Classify as IDC-like iv FIG 04 Clinical Pathway · Presentation to Treatment 1 Presentation (mass thickening) 2 Triple assessment (USS + mammo ± MRI) 3 Core biopsy (B5b) 4 MDT staging + extent MRI 5 Surgery (WLE mastectomy) 6 Adjuvant endocrine Rx MRI recommended pre-operatively for ILC due to higher risk of underestimation on mammogram and USS v FIG 05 Key Concepts & Related Entities Classic ILC Indian file pattern Pleomorphic ILC Aggressive variant grade 3 Bilateral ILC 10–15% at diagnosis MRI staging of ILC Preferred for extent of disease CDH1 mutation Hereditary diffuse gastric + ILC Peritoneal metastasis ILC-specific spread pattern vi FIG 06 Key Statistics · ILC ~15% of all invasive breast cancers [1] >90% ER-positive (endocrine therapy responsive) [2] 10–15% bilateral at diagnosis [3] ~85% MRI sensitivity vs ~65% mammogram [4] vii FIG 07 References 1. Makki J. Diversity of breast carcinoma. Clin Med Insights Pathol 2015 2. Christgen M et al. ILC molecular characteristics. Virchows Arch 2016 3. Pestalozzi BC et al. Bilateral ILC. J Clin Oncol 2008 4. Morrow M et al. MRI for ILC. JAMA 2007;298:1279 5. WHO Classification of Tumours: Breast 5th ed. IARC 2022 Clinically authored by Dr Fiona Tsang-Wright , FRCS (Gen Surg) GMC 4549831 · ORCID 0000-0003-4801-026X
Visual Reference · Invasive lobular carcinoma
Open full size ↗
Definition
Invasive lobular carcinoma is the second most common type of invasive breast cancer, accounting for around 10–15% of cases — a cancer that began in the milk-producing lobules and grows in a distinctive single-file pattern that can make it harder to detect on imaging.

Common questions The questions patients ask first

Is lobular cancer worse than ductal cancer?
On average, no. Lobular and ductal cancers have broadly similar outcomes when matched for size, grade, and other features4. The differences are in how the cancer is investigated and surgically planned, not in long-term survival.
Why am I being sent for an MRI?
Lobular cancer is sometimes more extensive than mammogram and ultrasound suggest, because the diffuse growth pattern can be subtle on those tests. MRI gives a more complete map of the cancer and can change the surgical plan35 — for example, identifying a second area in the same breast or in the other breast that needs assessment before surgery.
Is lobular cancer more likely to come back?
Recurrence depends on size, grade, lymph node status, and treatment, not on the lobular versus ductal label per se. Where there is a difference, lobular cancers tend to recur later than ductal cancers — sometimes 10 years or more after treatment4 — which is one reason long-term hormone therapy is often recommended2.
Will I need a mastectomy because it is lobular?
Not automatically. Many ILCs can be treated with lumpectomy plus radiotherapy5. The decision depends on the size and extent on imaging (including MRI), the patient's anatomy, and the patient's preferences — the same factors as for ductal cancer.

Invasive lobular carcinoma is the second most common type of invasive breast cancer, accounting for around 10–15% of cases (UK figures around 15%)1 — a cancer that began in the milk-producing lobules and grows in a distinctive single-file pattern that can make it harder to detect on imaging.

ILC behaves differently from the more common invasive ductal carcinoma (IDC) in three practical ways: it can be harder to feel, harder to see on a mammogram, and it tends to be more often bilateral or multifocal. The treatment principles are similar to IDC, but the diagnostic and surgical planning often involves additional imaging — particularly MRI.

Orientation Why you might be reading about this

You have probably been told that your biopsy shows lobular carcinoma, or you are reading to understand what makes lobular cancer different from the more common ductal cancer. ILC is a recognised subtype with specific features that affect how it is investigated and treated. This page explains those differences.

Related terms: Invasive ductal carcinoma · DCIS · Mammogram · Breast MRI · Mastectomy

Distinguishing features What makes lobular cancer distinct

Most breast cancers begin in the milk ducts and form a discrete lump. Lobular cancer begins in the lobules — the small glandular structures where milk would be produced — and tends to grow in a different pattern: not as a defined lump but as single-file lines of cancer cells infiltrating through the surrounding tissue.

This single-file growth pattern has several practical consequences:

  • It can be harder to feel. A lobular cancer often does not form the discrete, marble-like lump that ductal cancer typically presents as. Patients may notice an area of thickening or a vague change in breast texture rather than a specific lump.
  • It can be harder to see on a mammogram. Lobular cancers do not always produce the dense, well-defined image that mammograms pick up most reliably. They can be subtle or even invisible on standard imaging.
  • MRI is more sensitive for lobular cancer than for ductal cancer. Where ILC is suspected or confirmed, breast MRI is often added to mammogram and ultrasound to map the true extent of the cancer in the breast35 — this matters because the visible lump on standard imaging may underestimate the actual disease.
  • ILC is more often multifocal (more than one area in the same breast) or bilateral (in both breasts) than ductal cancer4, although bilateral cases remain uncommon.
  • Almost all ILCs are oestrogen-receptor positive.4 This usually means they respond well to hormone therapy2. HER2 positivity is uncommon in ILC.

When ILC does recur or spread, it can follow a distinctive pattern — more often involving the peritoneum (abdominal lining), gastrointestinal tract, or ovaries than conventional ductal cancer, in addition to bone and other usual sites. This matters for symptom awareness during follow-up.

These differences do not make lobular cancer “worse” than ductal cancer — outcomes are broadly similar — but they do mean the diagnostic and surgical pathway is sometimes more complex, with a stronger reliance on MRI before deciding on surgery.

Molecular profile The molecular signature

The defining cellular feature of lobular cancer is loss of E-cadherin, a protein that normally helps cells stick to each other1. Without E-cadherin, cancer cells lose their ability to stick together and end up infiltrating in single-file lines rather than forming clumps1. This molecular feature is what pathologists test for to confirm a lobular diagnosis.

The closely related lobular carcinoma in situ (LCIS) is a separate finding — not a cancer in the conventional sense, but a marker of raised future cancer risk in either breast. LCIS is sometimes seen alongside or near an invasive lobular cancer; it is also sometimes found on a biopsy of an unrelated benign-looking abnormality, and is then managed with surveillance rather than immediate surgery.

Treatment Treatment

The treatment principles for ILC are the same as for IDC: surgery (lumpectomy plus radiotherapy, or mastectomy with or without reconstruction), sentinel lymph node biopsy for invasive disease, and adjuvant treatment based on the cancer’s biology.

A few specific considerations:

  • Pre-operative imaging — many surgeons add MRI for ILC, even when mammogram and ultrasound seem clear, because of the higher chance that the visible disease underestimates the true extent.
  • Surgical margins can be more challenging in ILC because the diffuse growth pattern is harder to delineate — re-excision rates are slightly higher than for IDC, particularly for larger cancers.
  • Hormone therapy is almost always part of the plan because ILC is overwhelmingly ER-positive — typically for 5–10 years2.
  • Chemotherapy decisions are individualised; some genomic tests (Oncotype DX, MammaPrint) work well in ILC, others have specific caveats6. The MDT considers this when advising.
  • Long-term follow-up is the same as for any invasive breast cancer.

At consultation What to discuss with your surgeon

If your biopsy shows ILC:

  • Whether MRI is being done before deciding on surgery, and what additional information it might provide.
  • How likely a re-excision is, given the diffuse growth pattern of lobular cancer.
  • Whether mastectomy or lumpectomy is the better operation for your specific cancer — the multifocality and imaging-occult features of ILC sometimes shift the balance.
  • Surveillance of the other breast, given that ILC has a slightly higher rate of bilateral involvement than ductal cancer.

Because lobular cancer can be harder to map on imaging, a second-opinion consultation is a usual way to review the surgical plan before you decide.

Resources Further reading

Sources & guidance

Every figure on this page is anchored to a published source. Tap a number in the text or below to jump to the reference.

  1. reference text WHO Classification of Tumours Editorial Board. Breast Tumours. WHO Classification of Tumours, 5th edition, vol. 2. Lyon: International Agency for Research on Cancer. 2019 ;Invasive lobular carcinoma https://tumourclassification.iarc.who.int/ Cited for: Definition of invasive lobular carcinoma (single-file growth pattern, E-cadherin loss); proportion of invasive breast cancers (~10–15%); relationship to LCIS.
  2. meta analysis Early Breast Cancer Trialists' Collaborative Group (EBCTCG). Relevance of breast cancer hormone receptors and other factors to the efficacy of adjuvant tamoxifen: patient-level meta-analysis of randomised trials. The Lancet. 2011 ;378(9793):771–784 doi:10.1016/S0140-6736(11)60993-8 Cited for: Tamoxifen benefit in ER-positive breast cancer; rationale for 5–10-year endocrine therapy in ILC, which is overwhelmingly ER-positive.
  3. cohort Mann RM, Hoogeveen YL, Blickman JG, Boetes C. MRI compared to conventional diagnostic work-up in the detection and evaluation of invasive lobular carcinoma of the breast: a review of existing literature. Breast Cancer Research and Treatment. 2008 ;107(1):1–14 doi:10.1007/s10549-007-9528-5 Cited for: MRI is more sensitive than mammography and ultrasound for ILC; pre-operative MRI changes surgical planning in a meaningful proportion of cases.
  4. cohort Pestalozzi BC, Zahrieh D, Mallon E, et al. (International Breast Cancer Study Group). Distinct clinical and prognostic features of infiltrating lobular carcinoma of the breast: combined results of 15 International Breast Cancer Study Group clinical trials. Journal of Clinical Oncology. 2008 ;26(18):3006–3014 doi:10.1200/JCO.2007.14.9336 Cited for: ILC has comparable early outcomes to IDC but a later recurrence pattern; rationale for extended endocrine therapy.
  5. guideline National Institute for Health and Care Excellence (NICE). Early and locally advanced breast cancer: diagnosis and management (NG101). London: NICE. 2018 ;Last updated 2024; recommendation 1.2.4 — pre-operative MRI https://www.nice.org.uk/guidance/ng101 Cited for: UK indication for pre-operative MRI in invasive lobular carcinoma to map true disease extent.
  6. rct Sparano JA, Gray RJ, Makower DF, et al. Adjuvant chemotherapy guided by a 21-gene expression assay in breast cancer. New England Journal of Medicine. 2018 ;379(2):111-121 doi:10.1056/NEJMoa1804710 Cited for: TAILORx: 21-gene Oncotype DX recurrence-score-guided chemotherapy decisions in ER-positive HER2-negative early breast cancer (validated in ILC).