#1: Solid Tumor Rules (2018)
#2: Multiple primaries
Source 1: 2018 Solid Tumor Rules
pgs: 7, 24, 34
Notes: Breast; April 2019 Update
Solid Tumor Rules (2018)/Multiple Primaries--Breast: Is a breast resection showing invasive mucinous carcinoma in a single tumor with associated ductal carcinoma in situ and additional findings of a background of lobular carcinoma in situ single or multiple primaries and which M rule applies? See Discussion
Example: Right breast core biopsy found ductal carcinoma in situ in the upper outer quadrant. Subsequent resection has a final diagnosis of invasive mucinous carcinoma, grade 1, measuring approximately 7 mm, with close margins. See staging summary. Gross description mentions only the primary tumor with associated marker clip from previous biopsy.
Breast Cancer Staging Summary lists (testing and margins removed for brevity):
Procedure type: Lumpectomy.
Specimen laterality: Right.
Tumor size: 7mm.
Histologic type: Invasive mucinous carcinoma.
Histologic grade (Nottingham histologic score): Grade 1, (score 5/9).
Tumor focality: Single focus.
Lymph-vascular invasion: Not identified.
Treatment effect: No known therapy.
Ductal carcinoma in situ (DCIS): Present.
Architectural pattern: Cribriform.
Nuclear grade: Grade 1.
Necrosis: Not identified.
Calcifications: Not identified.
Estimated size/extent of DCIS: Spanning an area measuring 15mm.
Pathologic stage: pT1b, pNx. (AJCC 8th ed).
Distant metastasis: Not applicable.
Additional findings: Background lobular carcinoma in situ (LCIS), flat epithelial atypia (FEA), and atypical ductal hyperplasia (ADH).
Apply Breast Solid Tumor Rule M3, abstract a single tumor when there is a single tumor, as there is reference to the primary, single 7 mm tumor. Apply Rule H7 and code the invasive histology only, mucinous carcinoma, when both invasive and in situ components are present. The rules state: Do not use Table 2 Histology Combination Codes for tumors with both invasive and in situ behavior.