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Code to metaplastic carcinoma, 8575/3. According to our expert pathologist consultant, "The term 'metaplastic stroma' implies that at least a portion of the carcinoma has undergone a 'metaplastic' change from epithelial in appearance to 'stromal' in appearance. I assume this is what CAP means by 'Invasive mammary carcinoma with matrix production,' which the WHO equates to metaplastic carcinoma."

Abstract a single primary. Based on the information provided, this is a single tumor, and therefore a single primary, Rule M3. Code the histology to malignant phyllodes tumor.

According to our expert pathologist consultant, "The presence of a phyllodes tumor component identifies the whole thing as such. Stromal overgrowth/sarcoma is the usual identifier of malignancy in a phyllodes tumor. (If there were no phyllodes component we would be left with undifferentiated sarcoma, but that is not the case here. The diagnosis of malignancy in phyllodes tumor may be difficult/problematic when there is no overt stromal/sarcoma overgrowth as in this case.) As an aside, the behaviors of pure sarcoma and a phyllodes tumor such as we have here are similar, but we would lose the primary diagnosis if we just called this sarcoma."

For cases diagnosed 2007 or later, code 8523 [infiltrating duct mixed with other types of carcinoma] for

1. Infiltrating ductal carcinoma, mucinous type and

2. Infiltrating ductal carcinoma with features of tubular carcinoma

The infiltrating ductal types in Rule H12 are listed (8022, 8035, 8501-8508) and do not include mucinous or tubular. We cannot use this rule. The first rule that applies to these single tumors is H17, code to 8523. If you look up 8523 in the numerical morphology section of ICD-O-3, you will see similar examples included in the definition of this code.

Code the histology to ductal carcinoma, NOS [8500/3] for a pathology report with a final diagnosis of "invasive carcinoma, no special type." Do not code the histology to carcinoma, NOS [8010/3].

The 4th Edition of the WHO Classification of Tumors of the Breast refers to invasive ductal carcinoma as invasive carcinoma, no special type. The ICD-O-3 code remains the same as invasive duct carcinoma [8500/3]. The next revision to the MP/H Solid Tumor Rules will clarify this issue.

For a case diagnosed in 2003, code 8507/3 [Duct micropapillary carcinoma]. See Coding Complex Morphologic Diagnoses, revised August 2002, 3rd example on page 5 and page 3, #4.

For cases diagnosed 2007 or later, code 8507/3 [Duct micropapillary carcinoma]. Use rule H12.

Abstract a single primary using Rule M13. Assign 8523/3 using rule H29. The code for  invasive ductal carcinoma with tubular features (8523/3) is higher than the code for invasive lobular carcinoma (8520/3). H28 does not apply because 8523/3 is not included as a type of duct carcinoma on Table 2.

Code 8140 using rule H6. Rule H6 applies because the percent of mucinous is not specified.

Assign 8213/3 to invasive adenocarcinoma arising in a sessile serrated adenoma. The instruction in SINQ 20120089 is still valid. The 2014 ICD-O-3 Update does not change this SINQ answer.

For cases diagnosed 2007 or later, the correct histology code is 8244/3 [composite carcinoid]. 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 Colon Histology rules because site specific rules have been developed for this primary.

Step 2: Start at the SINGLE TUMOR module, rule H1. The rules are intended to be reviewed in consecutive order within a module. Stop at rule H9. Code the histology as 8244/3 [composite carcinoid] when the diagnosis is adenocarcinoma and carcinoid tumor.

Neuroendocrine tumor, grade 1 (G1) is synonymous with carcinoid tumor [8240/3] for the purpose of rule H9.

After consultation with our expert pathologist, the decision is report this case as a single primary. There was some confusion about how to apply the current MP/H rules to this pathology report given 1) the definition of M16 and M17 and 2) the likelihood for a single endometrial primary to present with several differentiations. According to our expert pathologist, "I would regard this case as a single endometrial primary with extensive endometrial involvement and several types of differentiation, all of which are seen in endometrial carcinomas."

Next, the Multiple Primary and Histology Coding Rules Manual is the correct source for coding histology for cases diagnosed 2007 or later.

The following steps are used to determine the histology code.

Open the Multiple Primary and Histology Coding Rules manual. For an endometrial primary, use the Other Sites Histo rules to determine the histology code because endometrium does not have site specific rules.

Start with the MULTIPLE TUMORS ABSTRACTED AS A SINGLE PRIMARY module, Rule H18. The rules are intended to be reviewed in consecutive order within the module from Rule H18 to Rule H31. You stop at the first rule that applies to the case you are processing.

Code the appropriate combination/mixed code (Table 2) when there are multiple specific histologies. GYN malignancies with multiple types of adenocarcinoma have histology coded to 8323/3 [mixed cell adenocarcinoma] per rule H30.