14.2 Solid Tumor Rules for Breast, Colon/Rectum & Lung: The Multiple Primary Rules in Order
Key Takeaways
Breast: bilateral breast cancer is multiple primaries (M7), a subsequent tumor in the same breast after more than five disease-free years is a new primary (M5), and carcinoma NST/duct plus lobular tumors in one breast are a single primary (M10).
Colon: FAP (or more than 100 polyps) with carcinoma is a single primary (M3), colon and rectum tumors are multiple primaries (M4), and tumors in different colon segments are multiple primaries (M9).
Colon anastomotic tumors are multiple primaries if they arise in the mucosa, are a NOS and its subtype, or occur more than 36 months after resection (M7); otherwise they are a single primary (M8).
Lung: a new tumor after more than three disease-free years is a new primary (M4), neuroendocrine plus non-small cell tumors are multiple primaries (M5), and simultaneous multiple tumors in one or both lungs are a single primary unless histologies differ (M9).
Lung M11 makes a single tumor in each lung two primaries unless there is proof one is metastatic; across all three modules, an invasive tumor more than 60 days after an in situ tumor is a new primary.
How to read these tables
Each table lists the Multiple Tumors rules for a module, in order. The Unknown and Single Tumor sections come first: a single tumor is always one primary, and "unknown if single or multiple" gives one primary. Remember the hierarchy: the first rule that applies decides the case.
Breast (C500–C509)
| Rule | Outcome | When |
|---|---|---|
| M4 | Multiple | Separate tumors in sites that differ at the 2nd or 3rd character (for example, C50 and C18) |
| M5 | Multiple | Subsequent tumor in the same breast after the patient was clinically disease-free for more than 5 years since diagnosis or last recurrence. A primary in the other breast does not restart the clock |
| M6 | Single | Inflammatory carcinoma in multiple quadrants of one breast, or in both breasts |
| M7 | Multiple | Bilateral breast cancer (right and left). A physician's phrase "bilateral breast cancer" does not make it one primary. Histologies may be the same or different |
| M8 | Single | Paget disease with synchronous underlying carcinoma NST (duct) or its subtypes |
| M9 | Multiple | Paget disease with an underlying tumor that is not duct (for example, lobular) |
| M10 | Single | Multiple tumors of carcinoma NST/duct and lobular (mixed 8522, or one duct and one lobular) |
| M11 | Single | Ductal carcinoma after a combination code in the same breast (for example, DCIS after DCIS plus LCIS 8522/2) |
| M12 | Multiple | Tumors that are two or more different subtypes/variants (column 3, Table 3). Timing is irrelevant |
| M13 | Single | Synchronous tumors on the same row of Table 3 (same code, synonym, or NOS plus its subtype) |
| M14 | Multiple | Tumors on different rows of Table 3, or a Table 2 combination code plus a Table 3 code |
| M15 | Single (the invasive) | In situ diagnosed after invasive in the same breast. Record the in situ as a recurrence |
| M16 | Single (the invasive) | Invasive 60 days or less after in situ in the same breast |
| M17 | Multiple | Invasive more than 60 days after in situ in the same breast |
| M18 | Single | None of the above |
Site coding reminders: multiple tumors in different quadrants of the same breast that are a single primary are coded C509, not C508. C508 is for a single tumor overlapping quadrants, or at 12, 3, 6 or 9 o'clock.
Worked case: a right breast lumpectomy in 2019 shows invasive carcinoma NST. In 2026 a new invasive carcinoma NST appears in the right breast after continuous disease-free follow-up. Seven years without recurrence meets M5, so the 2026 tumor is a new primary. If the tumor had appeared in the left breast in 2026, M7 would make it a new primary regardless of timing.
Colon, rectosigmoid and rectum (C180–C189, C199, C209)
| Rule | Outcome | When |
|---|---|---|
| M3 | Single | Adenocarcinoma (in situ or invasive) in at least one polyp and a clinical diagnosis of FAP, more than 100 polyps, or polyps "carpeting" the bowel. Site: C189 if more than one colon segment; C199 if colon plus rectosigmoid or rectum; C260 if colon plus small intestine. Multiple polyps alone are not FAP |
| M4 | Multiple | Sites differ at the 2nd or 3rd character, for example colon C18 and rectum C209 (not for FAP, and not for a single tumor overlapping colon and rectum) |
| M5 | Multiple | Two or more different subtypes/variants (column 3, Table 1). Timing irrelevant |
| M6 | Multiple | Different rows in Table 1. Timing irrelevant |
| M7 | Multiple | Subsequent tumor at the anastomosis when it is a NOS and a subtype of that NOS, or occurs more than 36 months after resection (24 months for pre-2022 cases), or arises in the mucosa |
| M8 | Single | Anastomotic tumor 36 months or less after resection, or arising in the wall or surrounding tissue without mucosal involvement, or documented as anastomotic recurrence. A rectal stump is an anastomotic site |
| M9 | Multiple | Separate tumors in sites that differ at the 4th character, meaning different colon segments (for example, sigmoid C187 and descending C186). Not used for C189 |
| M10 | Multiple | Subsequent tumor after being clinically disease-free for more than one year since diagnosis or last recurrence. Follow the rule even if the physician calls it a recurrence |
| M11 | Single | Synchronous tumors on the same row of Table 1 |
| M12 | Single (the invasive) | In situ after invasive. Record the in situ as a recurrence |
| M13 | Single (the invasive) | Invasive 60 days or less after in situ. Change the original behavior to /3 and keep the original date of diagnosis |
| M14 | Multiple | Invasive more than 60 days after in situ, even if the physician says recurrence |
| M15 | Single | None of the above. Example: in situ and invasive adenocarcinoma in the same segment |
Worked cases:
- Synchronous adenocarcinomas in the cecum (C180) and the sigmoid (C187), no FAP: M9 applies, giving two primaries.
- A patient with FAP has adenocarcinomas in polyps of the ascending and sigmoid colon: M3 applies, giving one primary, C189.
- A hemicolectomy was done in January 2024, and adenocarcinoma arises in the anastomotic mucosa in November 2025: M7 applies, giving a new primary, even though it is within 36 months.
Lung (C340–C343, C348, C349)
| Rule | Outcome | When |
|---|---|---|
| M3 | Multiple | Sites differ at the 2nd or 3rd character |
| M4 | Multiple | Subsequent tumor after being clinically disease-free for more than 3 years since diagnosis or last recurrence |
| M5 | Multiple | At least one neuroendocrine carcinoma or tumor (or subtype) and another tumor that is a non-small cell carcinoma subtype |
| M6 | Multiple | Two or more different subtypes/variants (column 3, Table 3). Timing irrelevant |
| M7 | Single | Synchronous tumors in the same lung on the same row of Table 3 |
| M8 | Multiple | Different rows in Table 3, or a Table 2 combination code plus a Table 3 code |
| M9 | Single | Simultaneous multiple tumors in both lungs (several on each side), in the same lung, or a single tumor in one lung with multiple tumors in the other. Exception: not if pathology proves different histologies, or if the attending physician, oncologist or pulmonologist states unequivocally that they are different primaries. Ambiguous terms such as "probable" do not count |
| M10 | Single (the invasive) | In situ after invasive in the same lung |
| M11 | Multiple | A single tumor in each lung, unless there is proof that one is metastatic (pathology comparison, or an unequivocal physician statement) |
| M12 | Single (the invasive) | Invasive 60 days or less after in situ in the same lung |
| M13 | Multiple | Invasive more than 60 days after in situ in the same lung, even if the physician calls it recurrence |
| M14 | Single | None of the above |
Worked cases:
- CT shows three adenocarcinoma nodules in the right lung and two in the left, all diagnosed together, and no physician calls them separate primaries: M9 applies, giving one primary. Laterality is 4 if the side of origin is unknown.
- A 2.1 cm right upper lobe adenocarcinoma and a 1.4 cm left lower lobe adenocarcinoma are found at the same time, and nothing proves either is metastatic: M11 applies, giving two primaries.
- A small cell carcinoma is found two years after a resected adenocarcinoma: M5 applies, giving two primaries. The M4 timing rule is not needed.
Timing summary
| Module | New primary if disease-free for more than |
|---|---|
| Colon, rectosigmoid, rectum | 1 year (M10) |
| Lung | 3 years (M4) |
| Breast, same breast | 5 years (M5) |
| In situ followed by invasive (all three modules) | 60 days |
Synchronous invasive carcinomas are found in the right breast (carcinoma NST) and the left breast (invasive lobular carcinoma). A physician documents "bilateral breast cancer." How many primaries are abstracted?
One, because the physician documents bilateral breast cancer
One, because M10 makes duct and lobular tumors a single primary
Two, because breast rule M7 makes bilateral breast cancer multiple primaries
Two only if the histologies are on different rows of Table 3
A patient has synchronous adenocarcinomas of the transverse colon (C184) and the rectum (C209), with no polyposis syndrome. Which rule applies first, and what is the result?
M9; multiple primaries because the colon segments differ
M4; multiple primaries because the site codes differ at the second and third characters
M11; a single primary because the histologies are the same
M3; a single primary coded to C199
A 1.8 cm right upper lobe adenocarcinoma and a 1.2 cm left lower lobe adenocarcinoma are diagnosed at the same time. Neither is proven metastatic, and no physician calls them separate primaries. How many primaries are abstracted?
One, under lung M9, because all simultaneous lung tumors are a single primary
Two, under lung M11, because there is a single tumor in each lung
One, under lung M7, because the tumors have the same histology
Two, under lung M4, because the tumors are in different lungs
Sections you finish are checked off in the contents.