Osteoarthritis (OA): Given the patient's age, post-menopausal status, and symptoms of chronic joint pain worse in hands with mild telescoping of digits and tenderness mainly at PIP joints, OA is a highly likely diagnosis. The absence of systemic symptoms and negative autoimmune panel further supports this diagnosis.

Psoriatic Arthritis (PsA): Although the autoimmune panel is negative, PsA can sometimes present without clear systemic symptoms or positive serologies. The presence of joint pain and tenderness, particularly at the PIP joints, along with the mention of mild telescoping (which could be interpreted as a form of dactylitis), makes PsA a consideration, especially if there's a history of psoriasis or other suggestive skin or nail changes.
Seronegative Rheumatoid Arthritis: Some patients with rheumatoid arthritis (RA) may be seronegative, meaning they do not have positive rheumatoid factor or anti-CCP antibodies. However, the clinical presentation and the absence of systemic symptoms or significant morning stiffness make this less likely compared to OA.

Paraneoplastic Syndrome: Given the patient's history of stable liposarcoma, it's crucial to consider the possibility of a paraneoplastic syndrome, which could manifest as joint pain among other symptoms. Although the cancer is described as stable, paraneoplastic syndromes can occur at any stage of cancer.
Infection (e.g., Septic Arthritis): Although less likely given the chronic nature of the symptoms, it's essential to rule out infectious causes, especially if there's any suspicion of recent trauma, injection drug use, or immunocompromised state.
Hematologic Malignancy (e.g., Multiple Myeloma): Elevated CRP can be seen in various conditions, including hematologic malignancies. Although rare, these conditions can present with joint pain and should be considered, especially with an elevated CRP and a history of cancer.

Relapsing Polychondritis: A rare autoimmune disorder characterized by recurrent episodes of cartilaginous inflammation, which could potentially involve the joints and lead to chronic pain.
Sjögren's Syndrome: Although the autoimmune panel is negative, Sjögren's can sometimes present with joint pain and should be considered, especially if there are other symptoms like dry eyes or mouth.
Ehlers-Danlos Syndrome (Hypermobility Type): Could be considered given the mention of mild telescoping of digits, but this would typically present with a broader range of symptoms including significant joint hypermobility and other systemic features.