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An endometrial cancer was diagnosed in 2018. The endometrial biopsy showed malignant mixed mullerian tumor (MMMT/Carcinosarcoma). The total abdominal hysterectomy/bilateral salpingo-oophorectomy showed Endometrial Carcinosarcoma (50% serous carcinoma, 50% high grade sarcoma with rhabdomyoblastic differentiation) with invasion of 100% of the myometrium and involvement of the uterine serosa. I am not finding this in the Solid Tumor Rules or the site-specific ICD-O-3 code lists.

The Solid Tumor Rules indicate bladder tumors that are urothelial carcinoma (8120) and small cell carcinoma (8041) are separate primaries per Rule M13 (Abstract multiple primaries when separate/non-contiguous tumors are on different rows in Table 2). These are distinctly different histologies and, presumably, one would want to capture the small cell carcinoma (or small cell carcinoma component) as this has a worse prognosis.

However, if a subsequent bladder tumor is composed of invasive urothelial carcinoma and small cell neuroendocrine carcinoma, the histology is coded as 8045/3 per Rule H4, but this is not abstracted as a multiple primary. The only M Rule that applies is Rule M18 (Abstract a single primary when tumors do not meet any of the above criteria). The mixed histology code 8045 is not included in Table 2, so none of the histology-based M Rules apply. Is the subsequent mixed invasive urothelial and small cell carcinoma tumor (8045/3) the same primary as a previously diagnosed invasive urothelial carcinoma (8120/3) when these tumors are diagnosed within three years?

It appears an argument could be made for both NLPHL (9659/3) and THRLBCL (9688/3). We favor coding NLPHL (9659/3) because the pathologist did specifically call this a Hodgkin lymphoma, and also specified that it only has a T-cell/histiocyte-rich large B-cell lymphoma-like pattern.

Table 6 (Tumors of the Oropharynx, Base of Tongue, Tonsils, Adenoids) in the Head and Neck Equivalent Terms and Definitions lists both squamous cell carcinoma HPV-positive and squamous cell carcinoma HPV-negative as subtypes/variants of squamous cell carcinoma (the NOS histology, 8070). Squamous cell carcinoma HPV-positive and squamous cell carcinoma HPV-negative are also listed in the 2018 ICD-O-3 update table.

Previous clarification from the standard setters regarding the 2018 ICD-O-3 Update table indicated that histology codes 8085 and 8086 (HPV-positive and HPV-negative squamous cell carcinoma, respectively) included p16+ and p16- squamous cell carcinoma, respectively. Presumably, this clarification was made because p16 is a surrogate marker for HPV, and capturing whether a tumor is HPV-related or not has implications for staging for 2018 and later diagnoses. However, this clarification was not added to the 2018 ICD-O-3 Update table via errata, nor do the Head and Neck Equivalent Terms and Definitions or Histology Coding Rules address this.

Is a diagnosis of p16-positive squamous cell carcinoma equivalent to a diagnosis of squamous cell carcinoma HPV-positive (8085)? If so, will this clarification be added to the Head and Neck Solid Tumor Rules?

Mixed odontogenic tumor consistent with dentinoameloblastoma, 9.5 cm, See Note: Tumor involves maxillary bone including hard palate, alveolar ridges, nasal cavities and maxillary sinuses bilaterally and buccal soft tissue. Lymphovascular invasion not identified. Perineural invasion not identified. Margins: Tumor involves right posterior bone (alveolar) margin. All other margins negative. Note: This is a rare hybrid tumor showing features of ameloblastoma producing pre-dentin/osteodentin matrix. Submucosal tumor is seen in the nasal cavities and palate. A congo red stain shows that the acellular dentin-like matrix fluoresces similar to collagen after polarization. Immunohistochemistry shows that the tumor cells are diffusely and strongly positive for p63, focally positive for CK19, and negative for CK5/6, SOX10, S100 and calretinin.

Since high grade squamous intraepithelial lesion (HGSIL) is reportable for the vulva in 2018 (per SINQ 20130185) but VIN II-III is not reportable, we need to clarify this reporting format seen in our area.

Example 1: 8/23/2017 debulking path diagnosis of low-grade appendiceal mucinous neoplasm (LAMN) with involvement of intrapelvic mucin, left ovarian mass, uterine serosa and pelvic tumor, consistent with disseminated peritoneal adenomucinosis, that may also be called low-grade mucinous carcinoma peritonei. 8/8/2018 resection of sigmoid and rectum, path diagnosis of peri-colorectal fibroadipose issue with low-grade mucinous carcinoma compatible with the prior diagnosis of pseumomyxoma peritonei with low-grade mucinous carcinoma histology.

Example 2: Path diagnosis of low-grade appendiceal mucinous neoplasm in association with low grade mucinous carcinoma peritonei involving the serosa of the small intestine and mesentery. Also, there is involvement of serosal lined soft tissue of peritoneum, omentum, stomach, falciform ligament, gallbladder, diaphragm and spleen.

Some pathologists in our area are referring to DPAM as mucinous carcinoma peritonei, which is causing confusion because the term carcinoma is being used. One would assume that because the pseudomyxoma peritonei/underlying tumor itself is low-grade (LAMN), then the case is not reportable, but we would like clarification.

Instruction number 1 under the Coding Multiple Histologies instructions states to code histology when the histology is described as subtype, type or variant. The general rules do indicate we can code the histology identified as type, but when applying the H Rules, it seems an argument could be made for either H1 or H3. H1 applies if you ignore the diagnosis of carcinoma and only code the histologic type: urothelial carcinoma. However, the rules do seem to imply that you take all histologies into account (e.g., code the subtype/variant when there is a not otherwise specified (NOS) and single subtype/variant). Following this logic, Rule H3 seems to be the only rule that fits, and one would code the subtype/variant urothelial carcinoma when the diagnosis is carcinoma NOS, histologic type: urothelial carcinoma.

The problem is that urothelial carcinoma is not a subtype/variant of carcinoma (NOS) per Table 2. The entry for Carcinoma NOS in Table 2 states, Subtypes of carcinoma NOS include adenocarcinoma and all subtypes/variants of adenocarcinoma. To some, urothelial carcinoma is a more specific type of carcinoma; however, urothelial carcinoma is not also listed as a subtype of carcinoma or of adenocarcinoma; only adenocarcinoma is categorized as a subtype of carcinoma. Consistently applying the rules becomes an issue when rules are interpreted in different ways. Should this Table be amended to include urothelial carcinoma as a subtype/variant of carcinoma NOS with the same caveat given to adenocarcinoma in Table 2?