Case Synthesis: Ms. Anju, 42-43F, Left Breast Lump (June 2025 - Aug 2026)

Timeline

The key teaching point: imaging-cytology discordance

• BI-RADS is a risk stratification system for imaging (Bailey & Love; Fischer's Mastery of Surgery):
  • 1 = negative, 2 = benign, 3 = probably benign (<2% malignancy, short-interval follow-up), 4a/4b/4c = suspicious (~2-10%, 10-50%, 50-95% malignancy risk respectively - biopsy mandatory), 5 = highly suggestive of malignancy (>95%), 6 = biopsy-proven malignancy (used once histology/cytology already confirms cancer, for staging/monitoring treatment response).
• A BI-RADS 4b lesion carries a real (10-50%) pretest probability of cancer. When the June 2025 FNAC came back benign ("old inflammatory lesion"), that is a discordant result - imaging said "moderately suspicious," cytology said "benign." The pathologist recognized this and explicitly recommended repeat tissue sampling/biopsy in the same report. This is standard practice: FNAC has a real false-negative rate from sampling error (needle missing the malignant focus within a heterogeneous mass), so discordant benign cytology in a BI-RADS 4/5 lesion should trigger a core needle biopsy (better than repeat FNA, since it preserves architecture for histologic grading and receptor testing), not reassurance.
• Recent literature (2025) specifically validates combining the Yokohama cytology system with BI-RADS to flag exactly this kind of discordance early - e.g., "Maximizing diagnostic precision: combined Yokohama and BI-RADS scoring for breast lesions" (PMID 39827505) and a 6-year correlation study (PMID 40520668), both showing that when cytology and imaging disagree, escalation to histology is what catches cancers that FNAC alone would miss.
• In this patient, it appears the recommended repeat biopsy was delayed by roughly 10 months. In that interval the mass grew from 7x5.3 mm to 20x15 mm and a suspicious axillary node appeared. The repeat FNAC in May 2026 finally confirmed malignancy (Yokohama C5).

• C1: Insufficient/inadequate
• C2: Benign
• C3: Atypical (probably benign)
• C4: Suspicious of malignancy
• C5: Malignant (this patient's May 2026 result) - large malignant cells, high N:C ratio, prominent nucleoli, necrosis/hemorrhage in the background are classic cytologic malignancy criteria, exactly as described in her report.

About the CA 15.3 values (both normal: 6.93 and 7.86 U/mL)

• CA 15.3 is not a screening or diagnostic test for breast cancer - sensitivity in early-stage, non-metastatic disease is poor. Even confirmed breast cancer patients frequently show normal pre-treatment CA 15.3.
• Its real utility is post-operative surveillance for recurrence/metastasis - a rising trend (>25% increase) suggests progression, and a >50% fall suggests treatment response. In combination with CEA, accuracy for monitoring improves to ~87%.
• So a normal CA 15.3 here is expected and does not argue against the biopsy-proven malignancy - it should instead be trended serially after treatment starts, as a baseline.

Where this patient stands now and what should happen next

1. Biopsy-proven (C5 malignant, cytology) carcinoma of the left breast
2. Interval growth of the primary lesion (7x5.3mm → 20x15mm over ~10 months) with spiculated/irregular margins - suggests infiltrative growth
3. A new suspicious axillary lymph node (10x7.5mm) - raises concern for nodal metastasis, needs its own FNAC/core biopsy for staging
4. BI-RADS 6 left, BI-RADS 1 right (unremarkable)

• Core needle biopsy of the breast mass (not just repeat FNAC) - to get histologic type, grade, and crucially ER/PR/HER2 status, since FNAC gives a cytologic diagnosis but not receptor profile or invasion status.
• Axillary node core biopsy/FNAC to confirm nodal status before surgery (affects staging and whether sentinel node biopsy vs axillary clearance is planned).
• Staging workup: CBC, LFTs, CT chest/abdomen or PET-CT, bone scan if indicated, baseline CA15.3/CEA for future monitoring.
• MDT referral: breast surgeon, oncologist, radiologist, pathologist to plan surgery (BCS vs mastectomy) +/- neoadjuvant therapy depending on size/nodal status/receptor profile.
• Address the identity discrepancy on the second CA 15.3 report before filing it in her records.

• Not a screening or diagnostic test for breast cancer. Sensitivity in early, localized disease is poor - many biopsy-confirmed breast cancers (like Anju's) have a completely normal CA 15.3 at diagnosis. This is exactly why her two CA 15.3 values (6.93 and 7.86 U/mL, both well under the 35 U/mL cutoff) don't contradict her cytology-proven carcinoma.
• Its real value is in post-treatment surveillance: monitoring for recurrence or metastatic disease after surgery. Sensitivity rises substantially in metastatic disease (roughly 54-87% in various studies).
• Trend matters more than a single value: a rise of >25% from baseline suggests disease progression; a fall of >50% suggests response to treatment.
• Often combined with CEA - together they improve monitoring accuracy (up to ~87% in some studies), and combined with CA 125 it can help detect ovarian cancer relapse too. It can also be mildly raised in colon, lung, and hepatic tumors, so it's non-specific.

• Regardless of the result, CA 15.3 should never be used as standalone evidence for presence or absence of malignancy - always interpreted alongside imaging and histology/cytology.
• Assay values aren't interchangeable across different lab manufacturers/methods.
• False positives/negatives can occur in patients who've received mouse monoclonal antibody therapy or diagnostics (interference).

BI-RADS Classification (Breast Imaging Reporting and Data System)

• June 2025: her mass was BI-RADS 4b → intermediate suspicion (10-50% risk of cancer) → correctly triggered "biopsy should be considered," which is why the FNAC was done.
• Her first FNAC came back benign, which was discordant with a 4b lesion (a 4b lesion still has up to 50% chance of being cancer, so a single benign cytology doesn't rule it out - this is why the pathologist recommended repeat biopsy).
• August 2026: now BI-RADS 6 - meaning imaging is simply documenting a mass that's already biopsy-confirmed malignant (from her May 2026 FNAC, Yokohama C5). At this stage BI-RADS 6 is used for pre-treatment staging and monitoring, not for diagnostic decision-making anymore - the diagnosis is settled; the remaining job of imaging is to define local extent (size, margins, nodal involvement) for surgical/oncologic planning.

• Category 4 is the only one split into sub-categories (4a/4b/4c) - this stratifies exactly how urgently biopsy is needed and helps counsel patients on real risk.
• BI-RADS applies to mammography, USG, and MRI alike - each modality gets its own BI-RADS score, which is why Anju had separate categorizations on her mammogram and ultrasound.
• BI-RADS 3 lesions are managed with surveillance (not biopsy) because the malignancy risk is low enough that watching is safe - this is a common exam trap (students often over-biopsy category 3).
• Right breast in her case was BI-RADS 1 (normal), confirming the disease is unilateral so far based on imaging.

What BI-RADS actually is

1. Roughly how likely this finding is to be cancer
2. What to do next (nothing, follow-up, or biopsy)

The categories, explained simply

• BI-RADS 0 - Incomplete. The radiologist needs more views, more imaging, or old films to compare against before they can even give a category. Not a final answer.
• BI-RADS 1 - Negative. Completely normal breast tissue. (This is what Anju's right breast was scored.)
• BI-RADS 2 - Benign. Something was seen (like a simple cyst or a calcified fibroadenoma) but it's clearly not cancer, just noted for the record.
• BI-RADS 3 - Probably benign. Risk of malignancy is very low (≤2%), but not zero enough to totally ignore. Management: don't biopsy yet, just repeat imaging in ~6 months to make sure it isn't changing.
• BI-RADS 4 - Suspicious. This is the "grey zone" category and it's split into three sub-grades because "suspicious" can mean very different things:
  • 4a = low suspicion (2-10% risk)
  • 4b = intermediate suspicion (10-50% risk) - this is what Anju's mass was initially
  • 4c = high suspicion (50-95% risk)
  • All of category 4, regardless of sub-grade, means: biopsy should be done. The sub-grading just tells you how worried to be while you wait for results.
• BI-RADS 5 - Highly suggestive of malignancy (≥95% risk). Basically, the radiologist is saying "this looks like cancer on imaging alone" - biopsy is mandatory, essentially confirmatory at this point.
• BI-RADS 6 - Already biopsy-proven cancer. This isn't a diagnostic category at all - it's used once a tissue diagnosis already exists (like Anju's May 2026 malignant FNAC), and repeat imaging is now just being used to plan treatment (measure the tumor, look for nodes, check the other breast) rather than to ask "is this cancer?"

Why the sub-categories of 4 matter clinically

Quick way to remember it for exams

• 0 = incomplete
• 1, 2 = normal/benign - routine screening
• 3 = probably benign - short-interval follow-up, no biopsy
• 4 (a/b/c) = suspicious - biopsy, with increasing urgency
• 5 = malignant until proven otherwise - biopsy
• 6 = already proven malignant - staging, not diagnosis