Breast Neoplasms

Benign lumps, scary mimics, and the red flags that separate them. From fibroadenoma to inflammatory carcinoma.🔑Two pivots on every stem: Is it MOBILE or FIXED? Does she have DISCHARGE? Those two cut the differential in half.

Cancer hub · HER2 / BRCA / SERMs · GYN Infections · Sexual Differentiation

A 42-year-old premenopausal woman presents with spontaneous unilateral bloody discharge from the left nipple. She has no palpable mass. Mammogram shows a single dilated duct without calcifications. Which of the following is the most likely diagnosis?
Invasive ductal carcinoma
Intraductal papilloma
Fibrocystic changes
Phyllodes tumor
Think of it like a tiny polyp growing inside a milk duct. Intraductal papilloma is the #1 cause of bloody/serosanguinous nipple discharge in premenopausal women. It sits inside a single duct, too small to feel, but it bleeds because its stalk has fragile blood vessels. IDC can also cause bloody discharge, but you would expect a hard mass or microcalcifications. Fibrocystic changes give you bilateral cyclic pain, not unilateral discharge. Phyllodes tumors are big, round, and do not discharge. Bloody nipple discharge + single dilated duct + no mass = intraductal papilloma until proven otherwise.

Clinical Images

Mammogram showing microcalcifications in DCIS
📷 Mammogram: clustered microcalcifications in DCIS · tap to expand
Breast ultrasound showing fibroadenoma
📷 US: well-circumscribed, mobile breast mass (fibroadenoma) · tap to expand
Peau d'orange skin change in inflammatory breast cancer
📷 Peau d'orange: inflammatory breast cancer skin change · tap to expand

The Lineup

Tap a card to reveal the full profile. Lock in the key clue first🔑Every card front has ONE diagnostic hook. That is the board question clue. Commit before you flip., details second.

🪨
Invasive Ductal Carcinoma
Most common (~75%). Irregular hard mass. Spiculated on mammogram.🔑IDC = "It's Definitely Cancer." Rock-hard + fixed + spiculated = IDC until proven otherwise.
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Invasive Ductal Carcinoma (IDC)
Freq~70-80% of all breast cancers; most common type
MassRock-hard, immobile, irregular borders; desmoplastic reaction
MammoSpiculated mass + clustered microcalcifications
SkinDimpling (tethered to Cooper ligaments)
ReceptorsTest ER, PR, HER2 on every biopsy specimen
ManageLumpectomy + radiation or mastectomy; SNB; systemic therapy per receptor
📊
DCIS
Microcalcifications only. No palpable mass. Non-invasive.🔑DCIS = "Danger Contained In Situ." Basement membrane still intact. The wall has not broken yet.
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Ductal Carcinoma In Situ
KeyMalignant cells inside duct; basement membrane INTACT
MammoClustered microcalcifications ONLY; no palpable mass
SubtypeComedocarcinoma = central necrosis; worst DCIS prognosis
RiskCan progress to IDC if untreated (pre-invasive)
ManageLumpectomy + radiation; tamoxifen if ER+
🧻
Invasive Lobular Carcinoma
Indian file pattern. Bilateral. No calcifications🔑ILC is the stealth cancer. Cells sneak single-file through stroma. Mammogram misses it because no calcifications. MRI is the better tool.. Easy to miss.
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Invasive Lobular Carcinoma (ILC)
Freq2nd most common (~10-15%)
PathSingle-file "Indian file" pattern; loss of E-cadherin
CalcificationsNONE (reason mammography misses it)
BilateralHigher bilateral risk than IDC
ReceptUsually ER+/PR+; rarely HER2+
ManageSame as IDC; MRI preferred over mammo for surveillance
🔥
Inflammatory Breast Cancer
Peau d'orange. Lymphatic invasion. Worst prognosis.🔑Not a mass. Looks like mastitis. Non-lactating + antibiotics fail = biopsy immediately. Every time. NOT a mass!
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Inflammatory Breast Cancer
KeyPeau d'orange (orange-peel skin), warmth, erythema; NO discrete mass
PathTumor emboli blocking dermal lymphatics
StageAlways T4d; typically Stage IIIB or higher
TrapMimics mastitis; non-lactating + antibiotics failed = biopsy
ManageNeoadjuvant chemo FIRST, then mastectomy + radiation (never surgery first)
🏳
Fibroadenoma
Young women. Mobile, smooth, rubbery.🔑"Breast mouse" = it runs away from your fingers. If you can chase it around, it's a fibroadenoma. No malignant potential.
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Fibroadenoma
Age15-35 years; most common benign breast tumor
MassRubbery, mobile, painless, well-circumscribed ("breast mouse")
HormonesEstrogen-responsive: grows in pregnancy, shrinks in menopause
Cancer riskNo malignant potential (unless complex variant)
ManageObserve if <3 cm and typical; excise if growing or atypical
🌿
Phyllodes Tumor
Large stromal + epithelial. Rapidly growing.🔑Phyllodes = fibroadenoma that went to the gym too much. Same fibroepithelial mix, but rapid growth + cystic areas on US = clue. Low-grade malignant potential.
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Phyllodes Tumor
Age5th decade (40s-50s)
MassLarge, rapidly growing, well-defined; leaf-like stroma on histology
USWell-circumscribed, hypoechoic with cystic regions
Malignant10-25% malignant potential (most are benign)
ManageWide local excision with margins; no axillary dissection needed
🤝
Intraductal Papilloma
Bloody nipple discharge. Single duct. No mass.🔑Like a nosebleed from a nasal polyp. One duct, one fragile stalk, one bleed. Unilateral bloody discharge + clean mammogram = papilloma.
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Intraductal Papilloma
AgePremenopausal (30s-50s)
Key ClueUnilateral serosanguinous/bloody nipple discharge; no mass
ImagingSingle dilated duct; usually invisible on mammogram
PalpableUsually NOT palpable
RiskSlight cancer risk; core needle biopsy needed
ManageDuct excision (microdochectomy)
📷
LCIS
Incidental finding. Bilateral risk marker.🔑LCIS is the weather advisory: conditions are risky. Not the storm itself. Bilateral risk, not a direct precursor. Invisible on imaging.
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Lobular Carcinoma In Situ
KeyIncidental on biopsy; no mass, no calcifications on imaging
TypeRisk marker, NOT direct precursor; bilateral cancer risk
GeneticsLoss of E-cadherin (lobular lesions lose E-cadherin; ductal retain it)
RiskIncreases risk in EITHER breast bilaterally
ManageSurveillance + tamoxifen chemoprevention; no surgery
🔴
Paget Disease of Breast
Eczematous nipple. Steroids fail.🔑Termites disguised as wood grain. Looks like eczema on the surface. Cancer underneath. Unilateral + steroid failure = biopsy, not more cream. Underlying DCIS or IDC.
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Paget Disease of Breast
KeyUnilateral eczema/crusting/erosion of nipple that does not respond to steroids
PathLarge Paget cells (clear halos) in nipple epidermis; PAS+
UnderlyingAlmost always associated with underlying DCIS or IDC
TrapBilateral = eczema. Unilateral + steroid failure = biopsy immediately
ManageFull workup for underlying malignancy; mastectomy or lumpectomy
🚕
Fat Necrosis
Post-trauma. Painless mass. Oil cyst with rim calcification.🔑Like a bruised avocado: damaged fat walls off into an oil cyst. Seatbelt injury + breast mass = fat necrosis first, cancer second.
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Fat Necrosis
AgeAny age; history of trauma (MVC, fall, surgery)
KeyPainless mass after breast trauma; CAN mimic cancer on exam
ImagingOil cyst (fat-density center); RIM calcification (not clustered)
PathLipid-laden macrophages, saponification, foreign-body giant cells
ManageObservation; benign, no cancer risk

Palpable Mass Workup

Walk the breast mass algorithm.🔑Two pivots: AGE determines first imaging (US vs mammogram). BI-RADS score determines biopsy vs follow-up. Learn those two forks and the tree writes itself. Make a call at each fork before the next step reveals.

Side-by-Side

Quick-reference comparison.🔑The three columns that matter most on boards: Age, Discharge type, Imaging pattern. Those three cut it to one diagnosis. Scroll horizontally on mobile.

Lesion Age Presentation Discharge Imaging Management
Fibroadenoma 15-35 Rubbery, mobile, painless None Solid, well-defined on US Observe or excise
Fibrocystic 25-50 Bilateral, cyclic pain Clear/straw Multiple cysts Reassurance, OCP
Papilloma 30-50 No mass, single duct Bloody Dilated duct on ductogram Duct excision
Phyllodes 40-50 Large, rapidly growing None Hypoechoic, cystic on US Wide excision
Fat Necrosis Any Post-trauma mass None Oil cyst, rim calcification Observation
DCIS 50-60 No mass (screening only) Rare Microcalcifications Lumpectomy + XRT
LCIS 40-50 Incidental on biopsy None Nothing (invisible) Surveillance + tamoxifen
IDC 55-65 Rock-hard, fixed mass Possible bloody Spiculated + microcalcifications Surgery + systemic
ILC 55-65 Subtle thickening, no mass None No calcifications; MRI preferred Surgery + systemic
Paget 50+ Eczematous nipple Possible Variable (underlying tumor) Mastectomy/lumpectomy
Inflammatory Any Peau d'orange, no mass None Skin thickening, diffuse Neoadjuvant chemo first

Elimination Round

Read the scenario. Eliminate wrong diagnoses one by one.🔑The elimination game builds the same reasoning the boards test: process of elimination, one clue at a time. Last one standing wins.

The Villains

Seven breast neoplasms. Each card front: the entity name and the single clue that makes it a board target. Flip for histology, clinical features, and the pearl that closes the question.

In Situ #1
DCIS

Ductal Carcinoma In Situ. Malignant cells packed inside ducts. Basement membrane intact.

Tap for histology and risk →
Board profile:
  • Histology: cribriform, comedo, or solid pattern; comedonecrosis in high-grade
  • Imaging: microcalcifications on mammogram
  • No invasion: basement membrane intact (not yet metastatic)
  • Risk: 25-50% progress to invasive ductal if untreated
  • Pearl: DCIS is the most common in situ carcinoma; often found on screening mammogram
In Situ #2
LCIS

Lobular Carcinoma In Situ. A risk marker, not a true cancer. Often bilateral and incidental.

Tap for the risk marker distinction →
Board profile:
  • Histology: small, dyshesive cells filling lobules; E-cadherin negative
  • No mass: not palpable, no mammographic finding
  • Risk: 10x increased risk of invasive cancer in EITHER breast
  • Bilateral risk: treat as a risk marker, not a pre-malignant lesion
  • Pearl: LCIS does not need clear surgical margins; management is surveillance
Invasive #3
Invasive Ductal Carcinoma

Most common breast malignancy overall. Hard, stellate mass with irregular borders.

Tap for presentation and pearl →
Board profile:
  • Most common: 70-80% of all breast cancers
  • Histology: glandular structures invading stroma; desmoplastic reaction
  • Gross: firm, gritty, stellate with irregular edges (spiculated on imaging)
  • Spread: axillary lymph nodes first, then lung, bone, liver, brain
  • Pearl: skin dimpling from Cooper's ligament tethering is a late sign
Invasive #4
Invasive Lobular Carcinoma

Second most common invasive type. Cells march in single file. E-cadherin negative.

Tap for the Indian file clue →
Board profile:
  • Histology: single-file (Indian file) pattern of cells in stroma
  • E-cadherin: negative (loss of cell adhesion molecule)
  • Bilateral: higher bilateral incidence than ductal
  • Spread: peritoneum, ovaries, GI tract, and meninges (atypical sites)
  • Pearl: may be missed on mammogram; MRI more sensitive
Invasive #5
Inflammatory Breast Carcinoma

Peau d'orange. Dermal lymphatic invasion without a discrete mass. Worst prognosis.

Tap for the lymphatic mechanism →
Board profile:
  • Mechanism: tumor cells block dermal lymphatics
  • Peau d'orange: skin looks like orange peel from lymphedema dimpling
  • No discrete mass: do not confuse with mastitis (no fever, does not respond to antibiotics)
  • Worst prognosis: Stage IIIB or IV at presentation
  • Pearl: young women, rapid onset. Biopsy the skin, not just the mass
Benign #6
Fibroadenoma

Most common benign breast tumor in women under 35. Rubbery, mobile, and well-circumscribed.

Tap for the board clue set →
Board profile:
  • Age: young women, ages 15-35
  • Feel: rubbery, freely mobile, well-defined, non-tender
  • Histology: proliferating stroma and ducts; no atypia
  • Hormonal: grows with estrogen (pregnancy), shrinks post-menopause
  • Pearl: does NOT increase cancer risk; management is observation
Invasive #7
Paget Disease of the Nipple

Eczematous, crusting nipple rash. Large Paget cells invade the epidermis from an underlying carcinoma.

Tap for the underlying cancer clue →
Board profile:
  • Appearance: unilateral eczematous rash of the nipple-areola; does not respond to topical steroids
  • Histology: large pale Paget cells with abundant cytoplasm in the epidermis
  • Always associated: underlying DCIS or invasive ductal carcinoma in over 95% of cases
  • Key clue: nipple involvement (not areola alone); unilateral
  • Pearl: biopsy the nipple, not the rash periphery. PAS-positive Paget cells confirm

Test Yourself

5 randomized questions from a bank of 10.🔑Read the last sentence of every stem first. That is where the question lives. Then hunt the stem for the one clue that answers it. All original.

Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last reviewed June 2026