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For tumors diagnosed prior to 2007:

Squamoid and squamous are synonymous. Squamoid is non-standard terminology. It means "squamous like" and is a synonym of squamous.

For tumors diagnosed 2007 or later, refer to the MP/H rules. If there are still questions about how this type of tumor should be coded, submit a new question to SINQ and include the difficulties you are encountering in applying the MP/H rules.

Assign histology code 8254/3.

The 2007 MP/H Lung rules do not include coding guidelines for mixed mucinous and non-mucinous tumors. Lung Table 1 (in the Terms and Definitions, pages 37-38, http://seer.cancer.gov/tools/mphrules/mphrules_definitions.pdf ) is very specific about which histologies can be coded to mixed adenocarcinoma (8255/3). Mucinous is not included per the note at the end of Table 1. Per WHO 3rd and 4th Ed Tumors of the Lung, mixed mucinous and non-mucinous tumors of the lung are classified as 8254/3.  Mixed invasive mucinous and non-mucinous adenocarcinoma is a synonym for BAC, mucinous and non-mucinous.

Code 8046 using Coding Instruction 2 that says to: Code the histology described as differentiation or features/features of ONLY when there is a specific ICD-O code for the "NOS with ____ features" or "NOS with ____ differentiation."

Note: Do not code differentiation or features when there is no specific ICD-O code.

In the example, no ambiguous terminology is used. If ambiguous terminology is used indicating a more specific term, you would code to the specific histology.

For tumors diagnosed prior to 2007:

According to SEER rules, abstract as one primary because although these sites have separate topography codes in ICD-O-3, they were coded to the same three-digit topography code in the first edition of ICD-O (SEER Program Code Manual, 3rd Edition, page 8, Exception B). Simultaneous lesions of the same histology in trachea and lung are one primary. Code the primary site to C399 [Ill-defined sites within respiratory system].

For tumors diagnosed 2007 or later, refer to the MP/H rules. If there are still questions about how this type of tumor should be coded, submit a new question to SINQ and include the difficulties you are encountering in applying the MP/H rules.

Code microwave tumor ablation as surgery. For lung, assign code 15.

This question was discussed by the technical advisory group – a small group of representatives from each standard setter which meets periodically. The group agreed on this consensus answer.

Most often when the invasive tumor and the in situ component are in the same lung and are the same histology, rule M12 (example 3) applies and this is a single primary. If the first wedge resection included part of the tumor and the in situ was not separate from the tumor, it is a single primary. We suspect that the margins were positive on the first wedge specimen which prompted the second wedge resection where the in situ was found. In addition, terminology for lung malignancies is undergoing change: what was called BAC (invasive) is now called adenocarcinoma in situ.

For cases diagnosed 2007 and later, accession a single primary, adenocarcinoma [8140/3] of the right lower lobe lung. The steps used to arrive at this decision are:

Step 1: Open the Multiple Primary and Histology Coding Rules Manual. Choose one of the three formats (i.e., flowchart, matrix or text). Go to the Lung MP rules because site specific rules have been developed for this primary.

Step 2: Start at the MULTIPLE TUMORS module, rule M3. The rules are intended to be reviewed in consecutive order within a module. Stop at rule M12. Accession a single primary when the patient has two tumors in the same lung with the same histology.

Keep in mind that physicians follow different "rules" to determine the number of primaries. Even though the physicians consider this case to represent two primaries, the MP/H rules instruct you to accession one primary.

We have received quite a few questions about the term lepidic. Below is the general definition of lepidic that will be added to the next MP/H revision.

"Lepidic" is a growth pattern meaning that tumor cells are growing along the alveolar septa. It is characteristic of bronchioloalveolar carcinoma (BAC), but not diagnostic of it. The diagnosis of BAC also requires no stromal, vascular, or pleural invasion. Lepidic growth may be seen in other adenocarcinomas, including metastases to lung from other sites. It is not a type/subtype of adenocarcinoma. For lepidic lung neoplasms, code the histology indicated, for example BAC.

Answer updated August 2025

Assign code 8044/3. WHO Classification of Thoracic Tumors, 5th edition, classifies SMARCA4-deficient malignant neoplasm as Thoracic SMARCA4-deficient undifferentiated tumor (SMARCA4-UT).